Slack microfrontend

[gchristov]

What does this pull request change?

This PR:

• splits up the /slack frontend into its own microfrontend using ExpressJS, adjusting the /slack/auth redirection to use the correct Slack client ID for the relevant environment (local/dev vs prod)
• deletes the /slack resources in landing-page-web-service
• moves the SlackConfig setup for slack-service to be in the domain module rather than adapter

How is this change tested?

Manually and with CI.

---

Writing Kotlin Multiplatform tests

[pulumi]

🍹 The Update (preview) for gchristov/landing-page-web-service/prod was successful.

Resource Changes

    Name                             Type                            Operation
~   landing-page-web-service         gcp:cloudrunv2/service:Service  update
~   landing-page-web-service-binary  docker:index/image:Image        update

[pulumi]

🍹 The Update (preview) for gchristov/proxy-web-service/prod was successful.

Resource Changes

    Name                      Type                            Operation
~   proxy-web-service         gcp:cloudrunv2/service:Service  update
~   proxy-web-service-binary  docker:index/image:Image        update

[pulumi]

🍹 The Update (preview) for gchristov/slack-web-service/prod was successful.

Resource Changes

    Name                      Type                            Operation
~   slack-web-service-binary  docker:index/image:Image        update
~   slack-web-service         gcp:cloudrunv2/service:Service  update

[pulumi]

🍹 The Update (preview) for gchristov/slack-service/prod was successful.

Resource Changes

    Name                  Type                            Operation
~   slack-service-binary  docker:index/image:Image        update
~   slack-service         gcp:cloudrunv2/service:Service  update