Fixes #420 - Add REST invocation function definition based on OpenAPI Path Object

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Discussion or Issue link:

See #647

What this PR does / why we need it:

In our latest Community Meeting, we discussed the possibility of adding support for RESTful operation descriptors in the Function definitions based on OpenAPI Path Item object. Here's the PR. The former PR has been closed.

Special notes for reviewers: The "Security Object" will be ignored by the specification since we already have the Auth Definition to fit this role. Two places to define the same information can be troublesome and error prune.

Additional information:

See reference: https://spec.openapis.org/oas/v3.1.0#paths-object