Move runner partition prefix to routable payload

Background

Runner partition prefix is introduced in !168017 (merged) for #442395

That's before !170634 (merged) is done for #489847 (closed)

Since routable token payload is designed to carry information, we can then move the prefix information into the payload.

Status as of 2025-03-06

At the moment we're not doing this. Relevant discussion can be found at gitlab-com/gl-infra/tenant-scale/cells-infrastructure/team#258 (comment 2376444164)

If we're doing this, we need to look at the followings:

• Update the documentation about payload information and size: https://handbook.gitlab.com/handbook/engineering/architecture/design-documents/cells/routable_tokens/
• Ensure that we do still have at least some form of prefix for runner tokens created via the registration token. Note that it cannot be glrt- because it has to be different than that to distinguish the workflow: gitlab-com/gl-infra/tenant-scale/cells-infrastructure/team#258 (comment 2377771524)
  • This is needed to make sure HTTP router can recognize it as a runner token rather than treating it as a personal access token
• Update HTTP router to make sure this new runner token format is recognized

We also have a proof of concept at: !183554 (merged)

Status Update

We moved the runner partition prefix to the payload, and added a new glrtr- prefix for registration token. With that, we can differentiate runner tokens from PAT.

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Action Items

• use glrtr- as the prefix for the registration token
• update the routable token documentation as per #523581 (comment 2408706798) - Explain t is runner type in routable_tokens.md (gitlab-com/content-sites/handbook!12602 - merged)
• address HTTP router rule change as per #523581 (comment 2408706798) - Update session_token rule for Runner tokens (gitlab-org/cells/http-router!590 - merged)
• Update the documentation to include the new prefix - Add new token prefix to docs (!186280 - merged)