getEnsembleIssueDates() and getEnsembleStartDates() in the EnsembleDatabase interface

[ktarbet]

I feel we should rename getEnsembleIssueDates() to getEnsembleStartDates(). (and return values from the start_datetime column)

getEnsembleStartDates() may be more appropriate for a minimal use case. In the test cases , in the code base, issue_datetime and start_datetime have been equivalent.

With DSS compatibility in mind I'm seeing issue_datetime as a 'version' of the data, that would map to the V tag in a F-part, and start_datetime maps to the T tag.

any thoughts?

[HenryGeorgist]

i think it makes sense to use get start date instead of get issuance date.

Though both are important.

we should add get issuance date, and replace current usage with get start date. but we should do that after current branches have been pruned.