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

.dockerignore

@@ -1,11 +1,14 @@
+
 # .git
 .codecov
 .github
 .gitignore
 .dockerignore
 **/Dockerfile
-/k8s/
-/node_modules/
+**/node_modules
+**/.pnpm-store
+**/.turbo
+**/.next
 /console/src/app/proto/generated/
 /console/.angular
 /console/tmp/
@@ -24,5 +27,5 @@ console/.angular
 console/node_modules
 console/src/app/proto/generated/
 console/tmp/
-.vscode
-build/*.Dockerfile
+build/*.Dockerfile
+