Update updated_at field when tags are changed #3319

Describe the Bug

The updated_at date in the json response (i.e. /api/pages) is not modified when the last update modifies only tags.
I think it would be more coherent to change this date when the tags are updated.
Moreover the tags are not listed in the list of elements queried (see #2680), therefore we cannot test for modified tags directly.

Steps to Reproduce

1. Create a page
2. Change only the tags (in a different commit)
3. Request the list of pages
   The updated_at date is the creation date instead of the tag modification date.

Expected Behaviour

I expect to have every actions listed in the commits to change the updated_at date. That is :

• Every content modification
• Every tag modification

Screenshots or Additional Context

I am using Bookstack v21.05.3.
I found the following related issues

• Add Tags and Plain Text Page Body to Pages Response API /api/pages  #2680 which would in a way solver the problem.
• pages.updated_at should only be updated when a revision is made, or the page "Updated by" date should use the latest revision #1777, focuses on sorting pages and updating the date but does not mention tags

Browser Details

No response

Exact BookStack Version

v21.05.3

PHP Version

No response

Hosting Environment

I unfortunnately do not know any information on the hosting environement.