chore: fix login integration (#10318)

# Which Problems Are Solved

Login integration tests are not executed in the pipeline

# How the Problems Are Solved

The login integration tests are fixed and added as a pipeline workflow.
It  tests against the built login docker image.
On pipeline failures, developers are guided on how to fix them using a
dev container configured for this purpose.

# Additional Changes

- email domains are replaced by example.com. In case the tests were
accidentally run against a cloud instance, it wouldn't cause bounces.
- pnpm is upgraded, because the --filter argument doesn't work for the
install command on the old version.
- The login Dockerfile is optimized for docker image builds

# Additional Changes From Review for
https://github.com/zitadel/zitadel/pull/10305

These changes were requested from @peintnermax 

- The base dev container starts without any services besides the
database and the dev container itself
- CONTRIBUTING.md is restructured
- To reproduce pipeline checks, only the devcontainer CLI and Docker are
needed. This is described in the CONTRIBUTING.md
- The convenience npm script "generate" is added

# Additional Context

- Follow-up for PR https://github.com/zitadel/zitadel/pull/10305
- Base for https://github.com/zitadel/zitadel/issues/10277

.devcontainer/base/Dockerfile

@@ -8,9 +8,13 @@ ENV SHELL=/bin/bash \
     PNPM_HOME=/home/node/.local/share/pnpm \
     PATH=/home/node/.local/share/pnpm:$PATH
 
-
 RUN apt-get update && \
     apt-get --no-install-recommends install -y \
+    # Cypress dependencies
     libgtk2.0-0 libgtk-3-0 libgbm-dev libnotify-dev libnss3 libxss1 libasound2 libxtst6 xauth xvfb && \
     apt-get clean && \
-    corepack enable && COREPACK_ENABLE_DOWNLOAD_PROMPT=0 corepack prepare pnpm@9.1.2 --activate
+    corepack enable && COREPACK_ENABLE_DOWNLOAD_PROMPT=0 corepack prepare pnpm@10.13.1 --activate
+
+COPY --chown=node:node commands /commands
+
+USER node