Mark unused&immature activitypub as "not implemented" (#36789)

After many years, "activitypub" is still "in progress" and no real
progress for end users. So it is not mature.

Temporarily mark the endpoints as "501 not implemented",
and wait until the whole design is stable and usable.

templates/swagger/v1_json.tmpl

@@ -23,58 +23,6 @@
   },
   "basePath": "{{.SwaggerAppSubUrl}}/api/v1",
   "paths": {
-    "/activitypub/user-id/{user-id}": {
-      "get": {
-        "produces": [
-          "application/json"
-        ],
-        "tags": [
-          "activitypub"
-        ],
-        "summary": "Returns the Person actor for a user",
-        "operationId": "activitypubPerson",
-        "parameters": [
-          {
-            "type": "integer",
-            "description": "user ID of the user",
-            "name": "user-id",
-            "in": "path",
-            "required": true
-          }
-        ],
-        "responses": {
-          "200": {
-            "$ref": "#/responses/ActivityPub"
-          }
-        }
-      }
-    },
-    "/activitypub/user-id/{user-id}/inbox": {
-      "post": {
-        "produces": [
-          "application/json"
-        ],
-        "tags": [
-          "activitypub"
-        ],
-        "summary": "Send to the inbox",
-        "operationId": "activitypubPersonInbox",
-        "parameters": [
-          {
-            "type": "integer",
-            "description": "user ID of the user",
-            "name": "user-id",
-            "in": "path",
-            "required": true
-          }
-        ],
-        "responses": {
-          "204": {
-            "$ref": "#/responses/empty"
-          }
-        }
-      }
-    },
     "/admin/actions/jobs": {
       "get": {
         "produces": [
@@ -1526,23 +1474,6 @@
         }
       }
     },
-    "/nodeinfo": {
-      "get": {
-        "produces": [
-          "application/json"
-        ],
-        "tags": [
-          "miscellaneous"
-        ],
-        "summary": "Returns the nodeinfo of the Gitea application",
-        "operationId": "getNodeInfo",
-        "responses": {
-          "200": {
-            "$ref": "#/responses/NodeInfo"
-          }
-        }
-      }
-    },
     "/notifications": {
       "get": {
         "consumes": [
@@ -21771,18 +21702,6 @@
       },
       "x-go-package": "code.gitea.io/gitea/modules/structs"
     },
-    "ActivityPub": {
-      "description": "ActivityPub type",
-      "type": "object",
-      "properties": {
-        "@context": {
-          "description": "Context defines the JSON-LD context for ActivityPub",
-          "type": "string",
-          "x-go-name": "Context"
-        }
-      },
-      "x-go-package": "code.gitea.io/gitea/modules/structs"
-    },
     "AddCollaboratorOption": {
       "description": "AddCollaboratorOption options when adding a user as a collaborator of a repository",
       "type": "object",
@@ -29513,12 +29432,6 @@
         }
       }
     },
-    "ActivityPub": {
-      "description": "ActivityPub",
-      "schema": {
-        "$ref": "#/definitions/ActivityPub"
-      }
-    },
     "AnnotatedTag": {
       "description": "AnnotatedTag",
       "schema": {