Align behaviour of after on AuditEvent repository and endpoint with Java Time's after methods

[wilkinsona]

The name after implies to me that if I pass in the exact time at which an event occurred then I will not see that event in the returned list as it did not occur after the given time. The name after and what it implies (to me at least) conflicts with how the parameter is documented in AuditEventRepository where it says that it is the "timestamp of earliest result required (or null if unrestricted)". The endpoint's HTTP API documentation is aligned with my interpretation of it being called after (unsurprising, as I wrote those docs). It describes the parameter as restricting the returned events "to those that occurred after the given time".

The current implementation is aligned with the parameter description. Rather than returning events that occurred after the given time, it returns events that occurred at the given time or later. As we move to using Instant (#10976) this confusion is likely to increase as its isAfter method returns false if the two instances being compared are equal.

I think we should keep the name after and align the behaviour with Java Time.