Add RepeatDateTimeList

[gmertes]

Description

The next ecflow release 5.17.0 will have a new RepeatDateTimeList. It creates a repeat from any list of strings in yyyymmddTHHMMSS format.

The difference with the existing RepeatDateTime is that the list doesn't need to be continuous nor uniform, offering more flexibility.

Contributor Declaration

By opening this pull request, I affirm the following:

• All authors agree to the Contributor License Agreement.
• The code follows the project's coding standards.
• I have performed self-review and added comments where needed.
• I have added or updated tests to verify that my changes are effective and functional.
• I have run all existing tests and confirmed they pass.