Allow users to unprotect environments

What does this MR do and why?

In the new UI, unprotecting a protected environment was left to last as it was an easy addition. The user is asked for confirmation before unprotecting.

Screenshots or screen recordings

How to set up and validate locally

1. Enable the feature flag:

Feature.enable(:multiple_environment_approval_rules_fe)

1. Navigate to a project's environments page Deployments > Environments
2. Add an environment
3. Navigate to the CI/CD settings page Settings > CI/CD
4. Protect the environment
5. expand environment block
6. unprotect environment

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.