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Co-authored-by: Jeremie Bresson <jeremie.bresson@unblu.com>

Use case: oauth2 access limited time tokens which should be updated on regular basis. Supplier allows us to move refresh logic outside client.
Use specified setter to set up supplier after gitlab api object creation.

This makes it possible to stream data coming
from another server straight into the POST request to Gitlab,
saving an extra, expensive, and useless IO operation on disk.

* Added Health Check API support