Allow the Issuer claim to be customizable for our Cloud Service Provider OIDC JWT tokens

Problem to solve

Customers that want to connect their runners to Cloud Service Providers via OIDC auth sometimes have their instances in protected environments (for example, not Internet connected).

The JWT token's issuer claim is set as the external URL which is pulled from the GitLab instance configuration.

Being able to customise the Issuer claim would allow customers to be able to use this functionality in a lot more environments.

There is a comment in this issue where the customer needs to be able to customise the Issuer Claim.

Proposal

Intended users

Feature Usage Metrics

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