Introduce CursorPager

What does this MR do?

For https://gitlab.com/gitlab-org/gitlab/-/issues/331493, as discussed in !68346 (comment 652611098)

This MR introduces the CursorPager class which helps to keyset paginate a given relation and also applies the header to the request that generates the link to the next page. The CursorPager wraps the generic keyset pagination library. We plan to use the CursorPager class to implement keyset pagination for various REST API endpoints.

No changelog added as this MR only introduces the service, but does not use it anywhere.

Screenshots or Screencasts (strongly suggested)

How to setup and validate locally (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

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• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.
• This change is backwards compatible across updates, or this does not apply.

Availability and Testing

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• I have tested this MR in all supported browsers, or it's not needed.
• I have informed the Infrastructure department of a default or new setting change per definition of done, or it's not needed.

Security

Does this MR contain changes to processing or storing of credentials or tokens, authorization and authentication methods or other items described in the security review guidelines? If not, then delete this Security section.

• 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