[BACKEND] Fix edit event endpoint to properly add timestamps

[choden-dev]

Is your feature request related to a problem? Please describe.

Right now in server\src\service-layer\controllers\AdminController.ts the editEvent method does not properly parse the timestamps, see the following example:

        sign_up_start_date: new Timestamp(
          body.data.sign_up_start_date.seconds,
          body.data.sign_up_start_date.nanoseconds
        ),

is how it should be done

BEFORE MERGING

• Integration test written for services
• Schemas annotated if adding new models
• Code generation run (hint: yarn workspace server tsoa spec-and-routes)
• Appropriate mocks created where possible
• PR Reviewed (For non-trivial changes)
• Changes tested after rebasing on master or merging in master (hint: git fetch origin master:master, then git rebase master or git merge master)
• All required PR checks passing