Instance homepage support (#4007)

* Prepare homepage parsers

* Add ability to update instance hompage

* Add ability to set homepage as landing page

* Add homepage preview in admin

* Dynamically update left menu for homepage

* Inject home content in homepage

* Add videos list and channel miniature custom markup

* Remove unused elements in markup service

server/controllers/api/custom-page.ts

@@ -0,0 +1,42 @@
+import * as express from 'express'
+import { ServerConfigManager } from '@server/lib/server-config-manager'
+import { ActorCustomPageModel } from '@server/models/account/actor-custom-page'
+import { HttpStatusCode } from '@shared/core-utils'
+import { UserRight } from '@shared/models'
+import { asyncMiddleware, authenticate, ensureUserHasRight } from '../../middlewares'
+
+const customPageRouter = express.Router()
+
+customPageRouter.get('/homepage/instance',
+  asyncMiddleware(getInstanceHomepage)
+)
+
+customPageRouter.put('/homepage/instance',
+  authenticate,
+  ensureUserHasRight(UserRight.MANAGE_INSTANCE_CUSTOM_PAGE),
+  asyncMiddleware(updateInstanceHomepage)
+)
+
+// ---------------------------------------------------------------------------
+
+export {
+  customPageRouter
+}
+
+// ---------------------------------------------------------------------------
+
+async function getInstanceHomepage (req: express.Request, res: express.Response) {
+  const page = await ActorCustomPageModel.loadInstanceHomepage()
+  if (!page) return res.sendStatus(HttpStatusCode.NOT_FOUND_404)
+
+  return res.json(page.toFormattedJSON())
+}
+
+async function updateInstanceHomepage (req: express.Request, res: express.Response) {
+  const content = req.body.content
+
+  await ActorCustomPageModel.updateInstanceHomepage(content)
+  ServerConfigManager.Instance.updateHomepageState(content)
+
+  return res.sendStatus(HttpStatusCode.NO_CONTENT_204)
+}