Check MaaS Admin Access

Checks whether the requesting user has MaaS admin privileges by performing a SelfSubjectAccessReview against the maasauthpolicies resource in the models-as-a-service namespace. Returns allowed: true only for users who can create MaaSAuthPolicy resources (i.e. cluster/MaaS admins). Token resolution priority:

1. Authorization: Bearer <token> — used by the ODH dashboard backend; correctly substituted with the impersonated user's token when the ODH dev impersonation feature (DEV_IMPERSONATE_USER) is active.

2. x-forwarded-access-token — fallback for standalone federated dev mode where the rspack proxy injects the real user's token directly.