Enable force experiment use for grape api endpoints

What does this MR do?

Enables consideration of request settings in the grape API layer for suggest_pipeline

This includes:

1. DNT browser settings.
2. Force Enable setting for easy testing in any environment without setting the feature in the database.

How this was noticed that was during testing locally, I noticed the force_experiment=suggest_pipeline wasn't entirely successful as seen in #267759

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

Closes #267759