Fixes last_audit_date not being stored via API correctly

[marcusmoore]

Description

This PR updates the StoreAssetRequest to put last_audit_date in a state that is valid for saving. The docs say that last_audit_date can be passed as a date but under the hood it needs to be stored as a datetime (#14472 introduced that validation).

If last_audit_date is provided, this PR uses Carbon to parse it and format it with a timestamp (always 00:00:00 even if the user provided a full datetime since that is the behavior we had previously) so it is savable.

Fixes the failing test that was introduced in #14472

Type of change

• Bug fix (non-breaking change which fixes an issue)

[shortcut-integration]

This pull request has been linked to Shortcut Story #25139: Fix last audit date test failure.

[what-the-diff]

PR Summary

• Refinement to StoreAssetRequest
  In the file named StoreAssetRequest.php, we've added functionality to automatically set the last_audit_date field (should it exist in the data being processed), and convert it to a standard date/time format for consistency.

• Alterations to AssetStoreTest
  Within the AssetStoreTest.php file, several changes were made to the testing of our asset storage:

  • The assertion for $asset->last_audit_date now ensures that this date is logged in a 'YYYY-MM-DD HH:MM:SS' format where 'HH:MM:SS' is always '00:00:00', signifying midnight.

  • Addition of testSetsLastAuditDateToMidnightOfProvidedDate method which verifies that when a last_audit_date is provided in the data, it's automatically set to the midnight of said date.

  • Addition of testLastAuditDateCanBeNull method to ensure that if the last_audit_date is not provided in the data, it should remain null in our database, avoiding incorrect data entries.