Split CiRunnerTokenAuthor class

What does this MR do and why?

Describe in detail what your merge request does and why.

This MR is the first of 3 MRs:

1. Split CiRunnerTokenAuthor class (!80621 - merged)
2. Refactor runner registration audit classes (!80623 - merged)
3. Log CI runner unregistration audit events (!79754 - merged)

It takes care of spliting the CiRunnerTokenAuthor class into 2 different classes:

• CiRunnerRegistrationTokenAuthor representing a runner registration token;
• CiRunnerAuthenticationTokenAuthor representing a runner authentication token.

Both classes inherit from CiRunnerTokenAuthor and add specific behavior to the respective type of token. This will be used in follow-up MRs.

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