[DOCS-5094] [CLI] Error thrown when using mutualTLS

[philsturgeon]

Running speakeasy merge on some of the documents in https://github.com/Mermade/openapi3-examples/ gave unexpected errors.

$ speakeasy merge --schemas=[/Users/phil/src/openapi3-examples/3.1/pass/mega.yaml] --out=test.yaml

Validating OpenAPI spec /Users/phil/src/openapi3-examples/3.1/pass/mega.yaml...

ERROR    validation error: [line 22] validate-security - security scheme mtls has invalid type 'mutualTLS' requires 'http', 'apiKey', 'oauth2' or 'openIdConnect'
failed validating spec /Users/phil/src/openapi3-examples/3.1/pass/mega.yaml	{"error":"\nOpenAPI spec invalid ✖"}

If Speakeasy CLI spots something it doesnt understand it would be best to just throw a warning if its relevant to the process being run, and ignore if not. I would expect merge to cope with seeing this and not worry too mcuh about what it means.

_DOCS-5094