Automatically set last updated date for assets and components

As per March 12th discussion on nexus-cma list.

Acceptance criteria:

• Adding a component or asset record will automatically set the last_updated property to the current time.
• Updating a component or asset record will do the same.
• Works for all types of repositories automatically. Accordingly, this work should also drop the code that manually sets this property today for nuget and raw assets.