[DEVOPS-1204] Migrate unified & it's build pipeline to self-host repo

[michalchecinski]

Type of change

- [ ] Bug fix
- [ ] New feature development
- [ ] Tech debt (refactoring, code cleanup, dependency upgrades, etc)
- [x] Build/deploy pipeline (DevOps)
- [ ] Other

Objective

Move unified to self-host repo: bitwarden/self-host#109

Code changes

• .github/workflows/build-self-host.yml: Remove build self host workflow
• docker-unified/:** Remove docker-unified

Before you submit

• Please check for formatting errors (dotnet format --verify-no-changes) (required)
• If making database changes - make sure you also update Entity Framework queries and/or migrations
• Please add unit tests where it makes sense to do so (encouraged but not required)
• If this change requires a documentation update - notify the documentation team
• If this change has particular deployment requirements - notify the DevOps team