Create new `gitlab_project_job_token_scopes` resource

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Closes #6206 (closed)

Instead of changing the types on the existing gitlab_project_job_token_scope resource, I'm going to create a new resource that accepts a list of target_projects instead of a single target_project_id. This allows us to handle both data types for a period of time, and I'll deprecate the existing resource until 18.0.

As a result, this isn't a breaking change, which means we also don't need to do any schema migrations for this, whereas attempting to update existing resources would have required designing a schema and state migration.