Improve detection of similarity sorting in GraphQL

What does this MR do?

This MR improves the detection of similarity sorting in GraphQL. Previously we were using a regex to look for an SQL pattern (/SIMILARITY\(/). This is error prone and could lead to false positives in the future.

The solution is to add a special SQL comment in the query that we can easily check later. The comment is added when generating the SIMILARITY() function.

Example expression:

ORDER BY (
/* gitlab/database/similarity_score */ SIMILARITY(COALESCE(path, ''), 'different') * CAST('1' AS numeric)) + 
(/* gitlab/database/similarity_score */ SIMILARITY(COALESCE(name, ''), 'different') * CAST('0.8' AS numeric)
) DESC, id DESC;

Other approaches (didn't work out):

• Use annotate from rails.
  • Unfortunately this adds comment to the end of the query. When detecting the sorting in GraphQL we only have access to the order expression (not the full query).
• Use Arel::Nodes::Comment to generate a comment string.
  • It's not possible to combine it with the existing Arel nodes (visitor call is missing).

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 #244853 (closed)