Expose deployment ids in response for a given environment

What does this MR do?

Fixes #33217 (closed)

In order to script actions against the Environments and Deployments APIs, additional endpoint features are needed. Using the API it should be possible to review details for all Deployment objects for a given Environment.

This MR:

• exposes a list of deployment IDs in Environment object

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