Move release evidence generation to service

What does this MR do?

Part of the #32773 (closed)

Extracted from !29255 (closed)

Release evidence generation needs to become a little more complicated:

1. it needs to preserve some build artifacts of the last pipeline(only reports) as part #32773 (closed)
2. it needs to be aware of this last pipeline because generating release actually pushes a new tag a spawns the new pipeline

So moving evidence generating to service sounds like a good idea to me.

That also resolves strange before_validation pattern which would regenerate evidence on any update(we don't do any updates currently, but still).

Some other ways to achieve the same goals:

1. Move this code to the worker class. But I wanted to keep it as simple as possible.
2. make before_validation .., on: create, add pipeline_id to model and another hook for preserving artifacts. But this would complicate the model.

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