Add GraphQL group timelogs time arguments

What does this MR do?

https://gitlab.com/gitlab-org/gitlab/-/issues/196834

Add start_time and end_time arguments in TimelogResolver to better reflect these field type and describe them as a timestamp.

As argument deprecation is not yet supported we are keeping start_date and end_date to prevent breaking changes. if these arguments are used the time will be set to end_of_day to avoid defaulting to 00:00:00 if time is not present.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done