[Vault-4628] OpenAPI endpoint not expanding root alternations

[VinnyHC]

Improve OpenAPI endpoint /sys/internal/specs/openapi to generate proper specs for path patterns that use an alternation as the root.
Example:

(creds|sts)/(?P<name>\w(([\w-.@]+)?\w)?)

should generate two paths in OpenAPI

creds/{name}
sts/{name}

[VinnyHC]

This was tested comparing the output from scripts/gen_openapi.sh -p when run against main and vinnyhc/VAULT-4628-OpenAPI. The only difference was the proper spec for the aws/creds/{name} entry.

[averche]

LGTM 👍