Fire webhook on deployment started
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### Problem to solve
<!-- What problem do we solve? Try to define the who/what/why of the opportunity as a user story. For example, "As a (who), I want (what), so I can (why/value)." -->
As we created a webhook for deployment events, we wanted to include started which will help users calculate cycle times with deployment activities.
### Proposal
Add started to webhook events
### Note
It's highly coupled with https://gitlab.com/gitlab-org/gitlab/-/issues/235475, so it will take less effort to work on these 2 issues simultaneously.
issue