Forms: Allow ability to add hidden fields

[coder-karen]

This is a work in progress

Fixes #21241

Proposed changes:

• This PR is a WIP, aimed at adding hidden fields to Jetpack Forms.
• Currently this includes:
  • The initial foundation added here: Forms: hidden fields #40329 (allows adding hidden fields via the inspector). Modifications to that include:
  • Creating a button to add new fields (allows for cases when the value field is blank)
  • Adding the hidden fields to form HTML if the value is blank for any name / value hidden field pairs, as well as a new filter, which allows third party integration for dynamically added values.
  • Warning messaging if duplicate names are spotted (but not preventing this from happening)
  • Ensures the Salesforce form variation uses a fixed-name hidden field to store the organization ID (and transfers existing organizationID attributes to the new hidden field), integrating with post-to-url to continue to allow posting to Salesforce. Currently we're not removing any existing Salesforce organizationID attribute values, but prioritizing the hidden field value instead (see below note).
  • A 'formID' attribute has been added, in preparation for future enhancements where we can create a UI for manually adding a unique form ID, or dynamically ensuring form IDs are unique (in order to be able to process hidden fields when there are more than one form on a page). See https://github.com/Automattic/vulcan/issues/601 for more details on how this could work with multiple forms on a page, in relation to hidden fields.

Features still to add:

• Consider re-usable hidden field 'templates'.
• Block deprecation additions due to new attributes.

Additional notes:

• Currently we're not removing any existing Salesforce organizationID attribute values, but prioritizing the hidden field value instead. What this means is that for existing forms, if someone were to accidentally delete the org ID and then save, refresh, it would automatically re-fill with the previously added org ID. That is currently both a pro and con, but I think a safer option may be to hold on to the old org ID for some releases, until any possible UI confusion has cleared - for example seeing the org ID under hidden fields as well, someone may delete it unknowingly initially. We will have to keep the organizationID attribute for backward compatibility anyway.

Other information:

• Have you written new tests for your changes, if applicable?
• Have you checked the E2E test CI results, and verified that your changes do not break them?
• Have you tested your changes on WordPress.com, if applicable (if so, you'll see a generated comment below with a script to run)?

Jetpack product discussion

#21241
See also https://github.com/Automattic/vulcan/issues/601

Does this pull request change what data or activity we track or use?

No.

Testing instructions:

TBD

Form response data and exporting data:

• After submitting a form that includes hidden fields, view the feedback response at wp-admin/edit.php?post_type=feedback and ensure the hidden field data is there.
• Try exporting the data via CSV, and Google sheets. In both cases, the hidden fields names should be prefixed with '85_', which will place them after the more important form data such as name, email, etc, but before Consent and IP address.

Salesforce integration testing:

• To test this, you'll want to confirm you can add new customers to Salesforce with an existing form (on trunk):
• Add a new Form block, but at the Salesforce Lead Form variation
• Under 'Organization ID' in the inspector (block sidebar), add your org ID. While there may be IDs / accounts available internally for testing, it is possible to sign up for a 30 day free trial with Salesforce. Finding your ID depends on the kind of dashboard you have, but this may help: https://help.salesforce.com/s/articleView?id=000385215&type=1
• Preview the form, and fill out the fields / submit.
• Check Salesforce 'Leads' to see if your new contact is added. If so, then you know the integration is working
• Then, apply this PR and revisit the form in the editor. Make sure there are no block validation errors, and that you can still see your org ID showing under 'Organization ID'.
• You should also be able to see it under 'Hidden Fields'. Editing both will be reflected in both areas. Try clearing the org ID and saving then refreshing - the original Org ID should repopulate.
• Test submitting the form again (with a different email address, otherwise you may get a Salesforce email to that address saying that a contact could not be added - though that is technically still confirmation that the Salesforce integration is working)
• Confirm the integration is still working.

[github-actions]

Are you an Automattician? Please test your changes on all WordPress.com environments to help mitigate accidental explosions.

• To test on WoA, go to the Plugins menu on a WordPress.com Simple site. Click on the "Upload" button and follow the upgrade flow to be able to upload, install, and activate the Jetpack Beta plugin. Once the plugin is active, go to Jetpack > Jetpack Beta, select your plugin, and enable the add/forms-hidden-field-option branch.

• To test on Simple, run the following command on your sandbox:

  bin/jetpack-downloader test jetpack add/forms-hidden-field-option
  

Interested in more tips and information?

• In your local development environment, use the jetpack rsync command to sync your changes to a WoA dev blog.
• Read more about our development workflow here: PCYsg-eg0-p2
• Figure out when your changes will be shipped to customers here: PCYsg-eg5-p2

[github-actions]

Thank you for your PR!

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