DRAFT Updating FlexibleDateTimeFormatter to cover edge cases

[arp-0984]

Adding extra date format patterns to cover edge cases and updating characters to remove from dates.

Testing with the new patterns covers all the edge cases I could find. I attempted to explain the new patterns in the config file. Utilizing DateTimeFormatter is tricky because it requires an exact match of a pattern to the provided date string. The goal here is not to be able to literally parse any date, but just match the behavior of the existing DateTimeFormatterLegacy class.

To do:

• fix unit tests
• expand unit tests to cover new patterns and characters to remove
• incorporate changes from https://github.com/NationalSecurityAgency/emissary/pull/763
• general cleanup