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/login-container.yml

@@ -12,8 +12,8 @@ on:
         type: string
     outputs:
       login_build_image:
-          description: 'The full image tag of the standalone login image'
-          value: '${{ inputs.login_build_image_name }}:${{ github.sha }}'
+        description: 'The full image tag of the standalone login image'
+        value: ${{ inputs.login_build_image_name }}:${{ github.sha }}
 
 permissions:
   packages: write
@@ -30,6 +30,8 @@ jobs:
     runs-on: ubuntu-latest
     permissions:
       packages: write
+    outputs:
+      login_build_image: ${{ steps.short-sha.outputs.login_build_image }}
     steps:
       - uses: actions/checkout@v4
       - name: Login meta
@@ -41,7 +43,7 @@ jobs:
           annotations: |
             manifest:org.opencontainers.image.licenses=MIT
           tags: |
-            type=sha,prefix=,suffix=,format=long
+            type=sha,prefix=,format=long
       - name: Login to Docker registry
         uses: docker/login-action@v3
         with:
@@ -49,6 +51,7 @@ jobs:
           username: ${{ github.actor }}
           password: ${{ secrets.GITHUB_TOKEN }}
       - name: Set up Docker Buildx
+        id: setup-buildx
         uses: docker/setup-buildx-action@v3
       - name: Bake login multi-arch
         uses: docker/bake-action@v6
@@ -58,13 +61,9 @@ jobs:
           source: .
           push: true
           provenance: true
-          sbom: true
           targets: login-standalone
-          set: |
-            *.cache-from=type=gha
-            *.cache-to=type=gha,mode=max
           files: |
             ./apps/login/docker-bake.hcl
-            ./apps/login/docker-bake-release.hcl
+            ${{ github.event_name == 'workflow_dispatch' && './apps/login/docker-bake-release.hcl' || '' }}
             ./docker-bake.hcl
             cwd://${{ steps.login-meta.outputs.bake-file }}