Implement support for runner token prefix

What does this MR do and why?

Describe in detail what your merge request does and why.

This MR adds support for the Ci::Runner model to have two types of authentication tokens: the usual one which will be created by Ci::Runners::RegisterRunnerService#execute, and a glrt- prefixed one which will be created by a future Ci::Runners::CreateRunnerService#execute.

Ci::Runners::RegisterRunnerService#execute is deprecated and will be removed in %17.0, so until then we need to be able to generate 2 types of tokens.

Closes #383198 (closed)

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