Prepare: run E2E smoketests with GitHub actions (#23301)

- Port E2E testing scripts from cypress-ui-automation
- Move server to docker-compose, move E2E images to ecrpublic
* Integrate General channel renaming, fixes
- Add local automation-dashboard
- Add readme
- Add E2E smoketests
- Bump postgres to 12

---------

Co-authored-by: Mattermost Build <build@mattermost.com>
Co-authored-by: Saturnino Abril <saturnino.abril@gmail.com>
Co-authored-by: Antonis Stamatiou <stamatiou.antonis@gmail.com>

server/build/gitlab-dc.schemapostgres.yml

@@ -1,7 +1,7 @@
 version: '2.4'
 services:
   postgres:
-    image: ${CI_REGISTRY}/mattermost/ci/images/postgres:10-1
+    image: public.ecr.aws/mattermostqa/postgres:12
     restart: always
     environment:
       POSTGRES_USER: mmuser
@@ -21,14 +21,9 @@ services:
           - postgres
 
   start_dependencies:
-    image: ${CI_REGISTRY}/mattermost/ci/images/mattermost-wait-for-dep:latest-1
+    image: mattermost/mattermost-wait-for-dep:latest
     depends_on:
       - postgres
     command: postgres:5432
     networks:
       default:
-
-networks:
-  default:
-    external:
-      name: ${COMPOSE_PROJECT_NAME}