[DOI-2682] Use UTCSentDate instead of UTCScheduleDate

[fgchaio]

Return the sent date in the campaign repository methods. Also, use sent date in the where of the queries.

Fixes: DOI-2682

Checklist:

• I have paid attention to this PR title and description
• I have performed a self-review of my code
• I have built it locally (or my changes does not affect the build)
• I have checked all tests still run ok at Doppler.ReportingApiTest project
• I have added at least one simple unit test covering the new code