[envvars-api] add messages to all responses
- openapi: rename v1.yaml to openapi.yaml
- openapi: add new model schemas
- openapi: refactor yaml
- build: add ResponseMessages to all responses
Bug: T356974
Depends-on: envvars-cli!38 (merged)
Signed-off-by: Ndibe Raymond Olisaemeka rolisaemeka-ctr@wikimedia.org