[FEATURE] Add specs for flow framework APIs

[dblock]

Is your feature request related to a problem?

The /_plugins/_flow_framework namespace is not included in the specs.

What solution would you like?

Add specs/tests for flow framework APIs, https://opensearch.org/docs/latest/automating-configurations/api/index/.

Do you have any additional context?

Part of https://github.com/opensearch-project/opensearch-api-specification/issues/168

[dbwiddis]

@junweid62 please comment here so we can assign this to you :)

[junweid62]

Sure thing! Commenting now. :)

[dbwiddis]

Resolved by #565