Update Service Account to indicate it is an administrator API call

What does this MR do and why?

Add the same Available only for administrators language from other administrator API calls to new Service Account API call

Issue where this was introduced:

Following API call is there for admins only and can be used for Self-managed

#406782 (closed)

Following API call is there for admins only and can be used for Self-managed

Feedback from Internal ZD Ticket

MR acceptance checklist

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