Add `description` param to the service access tokens

What does this MR do and why?

Add description param to the API endpoint that creates service access tokens.

In addition, we unify all the usage in a single place.

References

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• Closes Support `description` param for a personal acce... (#521379 - closed)

MR acceptance checklist

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Screenshots or screen recordings

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How to set up and validate locally

All current API endpoints to create access tokens should continue to work and support the description param:

• POST /api/v4/user/personal_access_tokens
• POST /api/v4/users/:user_id/personal_access_tokens
• POST /api/v4/groups/:group_id/access_token
• POST /api/v4/projects/:project_id/access_token

In addition, POST /api/v4/groups/:group_id/service_accounts/:user_id/personal_access_tokens should support description param.