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/commands/turbo-lint-unit.post-attach.sh

@@ -0,0 +1,30 @@
+#!/bin/bash
+
+if [ "$FAIL_COMMANDS_ON_ERRORS" == "true" ]; then
+    set -e
+fi
+
+echo
+echo
+echo
+echo -e "THANKS FOR CONTRIBUTING TO ZITADEL 🚀"
+echo
+echo "Your dev container is configured for fixing linting and unit tests."
+echo "No other services are running alongside this container."
+echo
+echo "To fix all auto-fixable linting errors, run:"
+echo "pnpm turbo lint:fix"
+echo
+echo "To watch console linting errors, run:"
+echo "pnpm turbo watch lint --filter console"
+echo
+echo "To watch @zitadel/client unit test failures, run:"
+echo "pnpm turbo watch test:unit --filter @zitadel/client"
+echo
+echo "To watch @zitadel/login relevant unit tests and linting failures, run:"
+echo "pnpm turbo watch lint test:unit --filter @zitadel/login..."
+echo
+
+if [ "$FAIL_COMMANDS_ON_ERRORS" != "true" ]; then
+    exit 0
+fi