Move API Reference (#23777)

* merge mattermost-api-reference unchanged

* api: update repostiory paths

* api: drop GitPod for api (for now)

* api: improved node_modules target

* api: relocate GitHub actions to root

* Update .github/workflows/api.yml

Co-authored-by: Antonis Stamatiou <stamatiou.antonis@gmail.com>

* fix cache-dependency-path

* adopt node-version-file

* pin versions for uses

* tidy steps/runs

* api/.gitpod.yml: tidy

* api: rm now unused .gitlab-ci.yml

---------

Co-authored-by: Antonis Stamatiou <stamatiou.antonis@gmail.com>

api/package.json

@@ -0,0 +1,25 @@
+{
+  "name": "mattermost-api-reference",
+  "version": "1.0.0",
+  "description": "This respository holds the API reference available at [https://api.mattermost.com](https://api.mattermost.com).",
+  "main": "index.js",
+  "dependencies": {
+    "redoc-cli": "0.13.17",
+    "swagger-cli": "4.0.4",
+    "sync-fetch": "0.4.1",
+    "yaml": "2.1.1"
+  },
+  "scripts": {
+    "test": "echo \"Error: no test specified\" && exit 1"
+  },
+  "repository": {
+    "type": "git",
+    "url": "git+https://github.com/mattermost/mattermost-api-reference.git"
+  },
+  "author": "",
+  "license": "ISC",
+  "bugs": {
+    "url": "https://github.com/mattermost/mattermost-api-reference/issues"
+  },
+  "homepage": "https://github.com/mattermost/mattermost-api-reference#readme"
+}