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

.github/workflows/lint.yml

@@ -53,14 +53,21 @@ jobs:
     steps:
       - name: Checkout
         uses: actions/checkout@v4
+      - name: Install Dev Container CLI
+        run: npm install -g @devcontainers/cli@0.80.0
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v3
-      - name: Run lint and unit tests in dev container
-        uses: devcontainers/ci@v0.3
-        with:
-          push: never
-          configFile: .devcontainer/turbo-lint-unit/devcontainer.json
-          runCmd: echo "Successfully ran lint and unit tests in dev container postStartCommand"
+      - name: Lint and Unit Test All JavaScript Code
+        run: npm run devcontainer:lint-unit
+      - name: Fix Failures
+        if: failure()
+        run: |
+          echo "Reproduce this check locally:"
+          echo "npm run devcontainer:lint-unit"
+          echo "If you have pnpm installed, most linting errors can be fixed automatically:"
+          echo "pnpm turbo lint:fix"
+          echo "In other cases, you can open the dev container called \"Turbo Lint and Unit Tests\"."
+          echo "You will have the same environment as the pipeline check as well as some guidance on how to fix the errors."
 
   core:
     name: core