Add connection redaction and connection extension methods

What does this MR do?

This prepares connections for the changes in !40088 (merged).

Specifically it adds:

• connection redaction support, so that we can do redaction of unauthorized results in a field extension.
• connection extension methods so that when we change the #resolve method in the graphql-helpers spec support module and tests suddenly receive connections rather than relations/arrays, they can still work in a somewhat transparent manner.

While this MR exists to support downstream work, the downstream MR is too large to merge as-is, and this section can be easily split out.

Screenshots (strongly suggested)

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