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

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

Dockerfile

@@ -6,7 +6,7 @@ COPY ./dist /dist
 WORKDIR /dist/assets
 RUN gzip -k ../index.html *.js *.map *.css *.wasm *-app-*.json 
 
-FROM nginxinc/nginx-unprivileged:alpine
+FROM nginxinc/nginx-unprivileged:alpine-slim
 
 COPY --from=builder ./dist /app