Allow to pass deployment_events to group hooks through the UI and API

What does this MR do?

Related to #238876 (closed)

We recently released #25344 (closed), but have forgotten about group interface for them.

Interface re-uses the same view, but the parameter is not whitelisted for group-webhooks.

So this MR:

• adds "deployment_events" to triggerable events for group
• adds it to controller whitelist(and refactors it a little)
• adds it the API params and response
• adds it to group hooks API docs

Also created an issue for unifying these codebases: #240940

Screenshots

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
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

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