Add spectral linter for Swagger (#20321)

[spectral](https://github.com/stoplightio/spectral) lints
openapi/swagger files for mistakes of which it has identified a few and
which I've fixed.

I had to put it into `lint-frontend` because it depends on node_modules
so can not run on Drone during the backend target. I plan to refactor
these targets later to `lint-js` and `lint-go` so that they are
categorized based on the tool dependencies.

templates/swagger/v1_json.tmpl

@@ -1131,9 +1131,7 @@
             "$ref": "#/responses/HookList"
           }
         }
-      }
-    },
-    "/orgs/{org}/hooks/": {
+      },
       "post": {
         "consumes": [
           "application/json"
@@ -16078,12 +16076,6 @@
       },
       "x-go-package": "code.gitea.io/gitea/modules/structs"
     },
-    "GitServiceType": {
-      "description": "GitServiceType represents a git service",
-      "type": "integer",
-      "format": "int64",
-      "x-go-package": "code.gitea.io/gitea/modules/structs"
-    },
     "GitTreeResponse": {
       "description": "GitTreeResponse returns a git tree",
       "type": "object",
@@ -16473,94 +16465,6 @@
       "x-go-name": "MergePullRequestForm",
       "x-go-package": "code.gitea.io/gitea/services/forms"
     },
-    "MigrateRepoForm": {
-      "description": "MigrateRepoForm form for migrating repository\nthis is used to interact with web ui",
-      "type": "object",
-      "required": [
-        "clone_addr",
-        "uid",
-        "repo_name"
-      ],
-      "properties": {
-        "auth_password": {
-          "type": "string",
-          "x-go-name": "AuthPassword"
-        },
-        "auth_token": {
-          "type": "string",
-          "x-go-name": "AuthToken"
-        },
-        "auth_username": {
-          "type": "string",
-          "x-go-name": "AuthUsername"
-        },
-        "clone_addr": {
-          "type": "string",
-          "x-go-name": "CloneAddr"
-        },
-        "description": {
-          "type": "string",
-          "x-go-name": "Description"
-        },
-        "issues": {
-          "type": "boolean",
-          "x-go-name": "Issues"
-        },
-        "labels": {
-          "type": "boolean",
-          "x-go-name": "Labels"
-        },
-        "lfs": {
-          "type": "boolean",
-          "x-go-name": "LFS"
-        },
-        "lfs_endpoint": {
-          "type": "string",
-          "x-go-name": "LFSEndpoint"
-        },
-        "milestones": {
-          "type": "boolean",
-          "x-go-name": "Milestones"
-        },
-        "mirror": {
-          "type": "boolean",
-          "x-go-name": "Mirror"
-        },
-        "mirror_interval": {
-          "type": "string",
-          "x-go-name": "MirrorInterval"
-        },
-        "private": {
-          "type": "boolean",
-          "x-go-name": "Private"
-        },
-        "pull_requests": {
-          "type": "boolean",
-          "x-go-name": "PullRequests"
-        },
-        "releases": {
-          "type": "boolean",
-          "x-go-name": "Releases"
-        },
-        "repo_name": {
-          "type": "string",
-          "x-go-name": "RepoName"
-        },
-        "service": {
-          "$ref": "#/definitions/GitServiceType"
-        },
-        "uid": {
-          "type": "integer",
-          "format": "int64",
-          "x-go-name": "UID"
-        },
-        "wiki": {
-          "type": "boolean",
-          "x-go-name": "Wiki"
-        }
-      },
-      "x-go-package": "code.gitea.io/gitea/services/forms"
-    },
     "MigrateRepoOptions": {
       "description": "MigrateRepoOptions options for migrating repository's\nthis is used to interact with api v1",
       "type": "object",