Resolve "Delete an environment via UI"

What does this MR do?

Adds a UI to delete an environment https://docs.gitlab.com/ee/api/environments.html#delete-an-environment

If an environment has been stopped, it displays a delete button in both the list and detail views.

Closes #20620 (closed)

Screenshots

List View

If an environment is running, the stop button is available:

If an environment is stopped, the delete button is available:

If the delete button is clicked, a delete modal appears. Clicking delete brings the user back to the environments page.

Detail View

If an environment is running, the stop button is available:

If an environment is stopped, the delete button is available:

If the delete button is clicked, a delete modal appears. Clicking delete brings the user back to the environments page.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Closes #20620 (closed)