Merge Auto DevOps beta template into the main template

What does this MR do?

Merges the workflow rules for early buildpack detection into the default Auto DevOps template and removes the feature flag that was created for easy rollback.

This feature has been live in production now for 3 releases (original issue #26655 (closed), original MR !20267 (merged)), but only for pipelines using Auto DevOps without a .gitlab-ci.yml.

With this change, projects that use include:template or create a new .gitlab-ci.yml from the CI template will also receive the workflow rules.

See #119025 (closed)

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