Support finding breaking change usage of environment.action `prepare` and `verify`

Problem to solve

As a GitLab user, I want to be safe when upgrade to GitLab 18.0.

The following issues introduce breaking changes in the environment.action behavior:

• Environment.action: access and prepare should r... (#437133 - closed)
• Environment.action: access and prepare should r... (#437133 - closed)
• Environment.action: access and verify should no... (#437142)

These are implemented behind the prevent_blocking_non_deployment_jobs feature flag.

Proposal

While the prevent_blocking_non_deployment_jobs is disabled, show a warning on every job that uses environment.action: prepare | verify.

Design

Implementation guide

For backend,

1. Add the environment action to BuildDetailsEntity.
2. Create a new deployment_options section which can hold the environment action (and anything else we might need later).

For frontend,

1. Add GlAlert to the job_app.vue or environments_block.vue

Copy:

The behavior of environment.action: prepare and environment.action: verify will change in GitLab 18.0. How do I keep the old behavior?

The link should go to the dedicated documentation page (TBD)

For documentation,

1. Add a new section explaining the changes and link to it from the banner.