feat: add support for asynchronous add and post methods

[JameelB]

This follows on from PR #208 which added initial support for asynchronous methods Delete and Update.

This adds 2 new asynchronous methods for Add and Post which will be used for generating endpoints for v1alpha1 of the aro_hcp API (see openshift-online/ocm-api-model#1047 (comment)).

[openshift-ci]

Hi @JameelB. Thanks for your PR.

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[JameelB]

PTAL @nimrodshn and @ahitacat 🙏

[ahitacat]

/lgtm
/approve

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ahitacat, JameelB

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[nimrodshn]

TY @JameelB 🙏

[miguelsorianod]

For now this is good enough but I want to raise awareness that this approach will fall short if for some reason we end up having some asynchronous endpoints that don't use HTTP 202, but 201. I mention this because the ocm api model is shared between offerings, not only aro-hcp.