Move deployment logic to deployable in EE

What does this MR do and why?

This MR is a follow-up of Move Deployment logic from Ci::Build to Ci::Dep... (!127079 - merged) that moves EE logic to deployable module.

It's a pure refactoring. No business logic changed.

Related to Support `environment` keyword with `trigger` ke... (#369061 - closed) Move Deployment logic from Ci::Build to Ci::Dep... (!127079 - merged) Include Ci::Deployable in Ci::Bridge (!127444 - merged)

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