ATLAS-5187: Fix audit related issues when rdbms backend is selected

[pinal-shah]

What changes were proposed in this pull request?

Issue1: Audit aging is not working

• Added new method to support it

Issue2: Null pointer while listing audits without action

• added check

Issue3: Audits doesn't gets sorted through 'user' or 'action'

• supported sorting through postgres query
• for action column which stores audit operation, Enum ordinal value was stored, this patch changes it to store Enum name. if not changed, we will have to sort inmemory to get correct results according enum name.

How was this patch tested?

manually