refactor: serve the api specs as plain json (#38715)

The api specs were Go templates whose committed form was not a valid
swagger document, so `swagger-validate`, `generate-openapi.go` and
`.spectral.yaml` each worked around it. They are now plain json,
substituted at serve time.

Renaming them off `.tmpl` also stops `make fmt` rewriting them, which
used to bump their mtime and silently skip the next `make
generate-swagger`.

Also enables stricter spectral linting: extends `lint-swagger` to the
OpenAPI 3 spec, turns on `openapi-tags`, `operation-singular-tag` and
`operation-tag-defined`, adds a top-level `tags` array with descriptions
to the swagger input, and drops the redundant `repository` tag from
`POST /user/repos`.

---------

Signed-off-by: silverwind <me@silverwind.io>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: Giteabot <teabot@gitea.io>

.github/workflows/files-changed.yml

@@ -113,8 +113,7 @@ jobs:
               - "Dockerfile.rootless"
 
             swagger:
-              - "templates/swagger/v1_json.tmpl"
-              - "templates/swagger/v1_input.json"
+              - "templates/swagger/*.json"
               - "Makefile"
               - "package.json"
               - "pnpm-lock.yaml"