fix: set created_at, updated_at fields before update in repo

[sudo-suhas]

These fields are saved to datastores in assets_versions table as well as the discovery repository. Populating the fields during insert/update ensures that the timestamps are synced across tables and datastores for a given asset.

[coveralls]

Pull Request Test Coverage Report for Build 4829312717

• 6 of 6 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.007%) to 85.808%

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Totals
Change from base Build 4739462284:	0.007%
Covered Lines:	5085
Relevant Lines:	5926

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💛 - Coveralls