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/v4/source/imports.yaml

@@ -0,0 +1,39 @@
+  "/api/v4/imports":
+    get:
+      tags:
+        - imports
+      summary: List import files
+      description: >
+        Lists all available import files.
+
+
+        __Minimum server version__: 5.31
+
+        ##### Permissions
+
+        Must have `manage_system` permissions.
+      operationId: ListImports
+      responses:
+        "400":
+          $ref: "#/components/responses/BadRequest"
+        "401":
+          $ref: "#/components/responses/Unauthorized"
+        "403":
+          $ref: "#/components/responses/Forbidden"
+        "404":
+          $ref: "#/components/responses/NotFound"
+      x-code-samples:
+        - lang: Go
+          source: >
+            import "github.com/mattermost/mattermost-server/v5/model"
+
+
+            Client := model.NewAPIv4Client("https://your-mattermost-url.com")
+
+            Client.Login("email@domain.com", "Password1")
+
+            imports, response := Client.ListImports()
+        - lang: Curl
+          source: |
+            curl 'http://localhost:8065/api/v4/imports' \
+            -H 'Authorization: Bearer 9kg8nqrnxprd9jbykqeg4r51hw'