Add GraphQL field spentAt to TimelogType and deprecate date field

What does this MR do?

Deprecate field date in favour of using spent_at, this would reflect better the attribute that we are linking to in the DB and the field type being a TimeType.

Field description was updated following styleguide.

Screenshots

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

Closes #213651 (closed)