refactor: project-wide change of OAS vendor extensions cactus -> cacti

[petermetz]

1. Did a complete find & replace of the old vendor extensions and the
   new ones. In theory this is a change that the compiler guarantees for us
   to verify completely, but even with that said, I'll leave the CI on so
   that we can double check to be sure.
   This is also a BREAKING CHANGE because if someone had installed the older
   packages and they imported endpoint definitions from the OAS spec based
   on the vendor extensions then their could would stop compiling. Therefore
   this change must be done before we issue the 2.0.0 release.
2. Also added a bug-fix to tools/custom-checks/check-open-api-json-specs.ts
   because it wasn't just validating HTTP verbs within "paths" but also
   any property that was in there such as "summary" or "description" but
   of course those are string properties so they won't pass the validation
   we impose on HTTP verb definitions for the endpoints.

Fixes #2872

Signed-off-by: Peter Somogyvari peter.somogyvari@accenture.com

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A Must Read for Beginners
For rebasing and squashing, here's a must read guide for beginners.

[outSH]

LGTM