Build Docker image on slim base (#3204)

* Build Docker image on slim base

* Run Playwright tests against Docker container

For Playwright end-to-end tests in CI, instead of running a development
webserver with `yarn dev`, build and deploy a Docker container for
Element Call and use that as the webserver to test against.

* Shut down playwright webserver gracefully

When using a containerized webserver, this stops the container once
tests finish.

* Increase Playwright timeout in CI

---------

Co-authored-by: fkwp <github-fkwp@w4ve.de>

scripts/playwright-webserver-command.sh

@@ -0,0 +1,10 @@
+#!/bin/sh
+if [ -n "$USE_DOCKER" ]; then
+    set -ex
+    yarn build
+    docker build -t element-call:testing .
+    exec docker run --rm --name element-call-testing -p 8080:8080 -v ./config/config.devenv.json:/app/config.json:ro,Z element-call:testing
+else
+    cp config/config.devenv.json public/config.json
+    exec yarn dev
+fi