Add regex fields to the container expiration policy update mutation

What does this MR do?

In !32944 (merged), a GraphQL update mutation for container expiration policies was added.

It was later find out that two input fields were missing (#196784 (comment 357409416)): name_regex and name_regex_keep. #220789 (closed) has been created to deal with this.

This MR adds them as input fields.

Design choices

• Note that in !34063 (merged), we added validation at the model level so that a container expiration policy can't be saved.
• We could just add the two missing input fields and let the model go 💥 when an invalid regex is passed
• We can also do a much better thing (implemented in this MR)
  • Add a GraphQL Scalar that will take a String and transform it into a String in both ways input <-> ruby code.
  • The Scalar will validate the string as an untrusted regex when coercing input -> ruby code.
  • The validation is based on the existing component: https://gitlab.com/gitlab-org/gitlab/-/blob/master/lib/gitlab/untrusted_regexp.rb
• The result is that the code flow doesn't execute the #resolve function of the mutation. The parameters are rejected by the GraphQL scalar itself = shorter code execution = several database requests saved = 🚀
• Nice bonus. Being a custom scalar, the type can be re-used by any other custom type.

Screenshots

GraphiQL editor:

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

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• 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