Add rich text format for custom fields

[cconard96]

Checklist before requesting a review

• I have read the CONTRIBUTING document.
• I have performed a self-review of my code.
• I have added tests that prove my fix is effective or that my feature works.

Description

Add option for custom text fields to support rich-text and images.

[orthagh]

Maybe not related to this pr, but I can't test it without this issue fixed:

[cedric-anne]

@cconard96 Please rebase to solve conflicts.

[cedric-anne]

1. The rendering of the default value is not correct:
   

2. When reopening the field configuration form, the default value is not rendered correctly in the modal :
   

3. Images are not converted correctly into document. This is usally done with a call to the CommonDBTM::addFile() in the post* methods.

4. We disabled the ability to put images in the task/followups/solutions/... templates because it was complicated to handle the copy of the corresponding document when an item was created using these templates. I think we should avoid usage of images in the default value here for the same reasons.

[orthagh]

Pending topic: if someone changes a field from rich-text to text-only, what do we do with the content?

• nothing, we consider the case rare
• we make a transformation to remove all tags and keep only text (Glpi\RichText\RichText::getTextFromHtml)
• we remove the slider and move to 2 field types to avoid this case (it may ease migration also as plugins separate these types of fields also)

@cconard96 your opinion?

[cconard96]

Pending topic: if someone changes a field from rich-text to text-only, what do we do with the content?

* nothing, we consider the case rare

* we make a transformation to remove all tags and keep only text (`Glpi\RichText\RichText::getTextFromHtml`)

* we remove the slider and move to 2 field types to avoid this case (it may ease migration also as plugins separate these types of fields also)

@cconard96 your opinion?

My opinion is not to bother modifying any of the values in the database if the field is switched between plain/rich text. If the field is plain text, we should force the displayed value to go through "getTextFromHtml". This way, simply switching to plain text and then back to rich text won't ruin existing values but if an asset is saved the plain version will be saved.

Second option would be just blocking changing this option once a field is created but it could limit usability. Admins would need to create a new field if they change their mind later and we don't offer any way to migrate data from one field to another.

[cedric-anne]

My opinion is not to bother modifying any of the values in the database if the field is switched between plain/rich text. If the field is plain text, we should force the displayed value to go through "getTextFromHtml". This way, simply switching to plain text and then back to rich text won't ruin existing values but if an asset is saved the plain version will be saved.

Seems a good way to handle it.

[orthagh]

let's go with that