Support OAuth authentication for publishing IG

[jecos]

With this PR, fhirutil CLI supports oauth authentication for publishing an implementation guide. There is 4 new options for publish command :

• oauth-url: URL of OAuth token endpoint
• oauth-client-id: id of the client to use to authenticate
• oauth-client-secret: corresponding secret
• oauth-uma-audience: (Optional) audience to use in case fhir server need a Request Party Token (RPT)

Example:

❯ fhirutil publish --base_url http://localhost:8080/fhir \
          --oauth-url https://localhost:8180/auth/realms/myrealm/protocol/openid-connect/token \
          --oauth-client-id my_client_id \
          --oauth-client-secret my_secret site_root/input/resources/search