Openmrs extra http wrappers

[PiusKariuki]

Summary

post remove and get helpers for HTTP
Fixes #

Details

Added wrappers, with tests and documentation, for http.get(), http.post() and http.remove.

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Review Checklist

Before merging, the reviewer should check the following items:

• Does the PR do what it claims to do?
• If this is a new adaptor, added the adaptor on marketing website ?
• If this PR includes breaking changes, do we need to update any jobs in
  production? Is it safe to release?
• Are there any unit tests?
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  dev only changes don't need a changeset.
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