Get Workshop/Gitlab number of users for an organization

In order to display gitlab usage, we want the billing service to get user seats for an organization.

Acceptance Criteria

• GIVEN [a precondition]
  AND [another precondition] WHEN [test step]
  AND [test step]
  THEN [verification step]
  AND [verification step]

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Security considerations

[note any potential changes to security boundaries, practices, documentation, risk that arise directly from this story]

Implementation sketch

[links to background notes, sketches, and/or relevant documentation

• [first thing to do]
• [another thing to do]