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>

e2e-tests/.ci/dashboard.entrypoint.sh

@@ -0,0 +1,21 @@
+#!/bin/bash
+set -e -u -o pipefail
+
+npm install
+
+# Run migrations. This is also a way to wait for the database to be up
+MIGRATION_ATTEMPTS_LEFT=10
+MIGRATION_ATTEMPTS_INTERVAL=10
+until npm run migrate:latest; do
+	MIGRATION_ATTEMPTS_LEFT=$((MIGRATION_ATTEMPTS_LEFT - 1))
+	[ "$MIGRATION_ATTEMPTS_LEFT" -gt 0 ] || break
+	echo "Migration script failed, sleeping $MIGRATION_ATTEMPTS_INTERVAL"
+	sleep $MIGRATION_ATTEMPTS_INTERVAL
+done
+[ "$MIGRATION_ATTEMPTS_LEFT" -gt 0 ] || {
+	echo "Migration script failed, exhausted attempts. Giving up."
+	exit 1
+}
+
+# Launch the dashboard
+exec npm run dev