Copy approvals from previous release

[kitallis]

Context

We recently added a feature #662 to assign approvals to a release. These approvals block the submissions/rollouts for a release until they are completed / overriden.

We would like to enhance this feature to have Tramline copy approvals from the previous release so that users don't have to remember to assign and type them out again every release.

Requirements

This involves two things:

First, add a configuration (enable/disable toggle) in the train/release settings page, under the approvals section:

• This would be a enable/disable toggle "Always copy approvals from previous release".
• This setting will automatically copy over the approvals from the previous release in the next release when it starts.
• With this setting, the approvals should not be copied over when it's a hotfix release.
• This setting should be off by default.
• This setting will show up only when the approvals checkbox is enabled.

Second, we should also allow copying approvals from within the release through a (currently disabled) button on the Approvals page This button should only show up and work when there are no approvals in the release, to avoid double-copying approvals.

Acceptance Criteria

• Use the SwitchComponent to implement the enable/disable toggle.
• Use the child switch functionality in the SwitchComponent.
• When approvals are automatically copied over via the setting, the copy should happen in a background job.
• Copying over approvals should send email as normal to assignees.
• When there's nothing to copy, it should do nothing (for example, no previous release or no approvals from before).

Additional notes

Currently, the + Add button is disabled for certain states of the release – stuff after the submission has started. This check should exist for the copy button as well.

[gitstart-connector]

Issue synced into GitStart. Please review, edit and hand it off to GitStart by following this link.

[gitstart-connector]

This issue has been handed off to GitStart: https://clients.gitstart.com/tramline/11653/tickets/TRAB-684