Expose `:release` yaml as steps via API

What does this MR do?

Satisfies part 2 of #199250 (closed):

Expose Release steps via the API

Currently the API exposes only the script and after_script steps, i.e. it is possible to called the releaser-cli like this:

{
    "steps": [
        {
            "name": "script",
            "script": [
                "job script",
                "release-cli create --name \"Release $CI_COMMIT_SHA\" --description \"Created using the release-cli $EXTRA_DESCRIPTION\" --tag-name \"release-$CI_COMMIT_SHA\" --ref \"$CI_COMMIT_SHA\""
            ] 
        }
    ]
}

Going forward we can name the steps, in this the step would be named release:

{
    "steps": [
        {
            "name": "script",
            "script": [...] 
        },
        {
            "name": "release",
            "script": [
                "release-cli create --name \"Release $CI_COMMIT_SHA\" --description \"Created using the release-cli $EXTRA_DESCRIPTION\" --tag-name \"release-$CI_COMMIT_SHA\" --ref \"$CI_COMMIT_SHA\""
            ]
        }
    ]
}

Please note:

• the yaml has already been validated before the pipeline is executed
• the :release node is currently behind a feature flag
• runner has been extended with this MR
• full description of the yaml is on the issue

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation !19237 (merged)
• 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

Part of #199250 (closed)