[FAU-441] Inclusion of Timestamps in Existing Degree Program API Responses

[shvlv]

Please check if the PR fulfills these requirements

• The commit message follows our guidelines
• Tests for the changes have been added (for bug fixes/features)
• Docs have been added/updated (for bug fixes/features)

What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)
Feature.

What is the current behavior? (You can also link to an open issue here)
https://inpsyde.atlassian.net/browse/FAU-441

What is the new behavior (if this is a feature change)?
date and modified fields were added to the fau/v1/degree-program and fau/v1/degree-program/{$id} endpoints.
date is a formatted WordPress core value, and modified is a custom meta value updated on any core or shared degree program properties changes.

The CacheInvalidated event was extended to add information about the reason why the cache was invalidated:

• enforced is a default value and used when cache invalidation happens with the admin bar or CLI
• data_changed points that cache invalidation is caused by any of the degree program data changes

View and Timestamp repositories work even if we have no date and modified cached values. In theory, we could provide a migration to set up those values after the plugin upgrade, but I think it's unnecessary, and the current implementation is more robust. Also, timestamps are not used for revision calculation, so nothing breaks.

Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?)

Other information:

• [FAU-441] feat: update modified value if any of degree program properties were updated FAU-Studium#147
• [FAU-441] feat: update container definition for view repository FAU-Studium-Embed#41

[amiut]

LGTM, thanks a lot for taking care of it.

[tyrann0us]

Thank you! Left a minor comment that doesn't stop me from approving.