Refactor environment model for bridge jobs

What does this MR do and why?

This MR is a follow-up of Refactor `Deployment` compatible with `Ci::Buil... (!128192 - merged). It refactors Environment model to be compatible with both Ci::Build and Ci::Bridge models.

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

Related to Support `environment` keyword with `trigger` ke... (#369061 - closed)

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