Support the configuration of JH separate database

What does this MR do and why?

Related issue: https://jihulab.com/gitlab-cn/gitlab/-/issues/3644

Use Rails multiple databases feature to implement JH database support.

This MR is based on the Upstream MR: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/133566

Reference

• Gitlab Database Schema: https://docs.gitlab.com/ee/development/database/multiple_databases.html#gitlab-schema

Implementations

Gitlab Rails

• config database.yml with :jh database
• add JH::ApplicationRecord as base class for JH models
• add JH::NamespacedModelName mixin to preserve model_name JH models
• introduce :gitlab_jh schema similar to the :gitlab_geo to deal with SQL cross-joins and cross-transactions
• migration/schema files are placed into jh/db/{xxx} folders
• support rails db:*:jh related tasks

CI jobs

• add global.gitlab-ci.yml to override default-before_script action
• override scripts/prepare_build.sh and util.sh to inject JH database in CI workflow
• override three CI database yaml with JH database config

How to set up and validate locally

1. create jh/db/migrate and jh/db/schema_migrations folders if they're not exist
2. copy jh/config/database.yml.example contents into config/database.yml, modify it to fit your local development env
3. run bundle exec rails db:create:jh to create JH database
4. (optional)you can run bundle exec rails g migration CreateJHHats name:string --database jh to create a demo table migration
5. (optional)then run bundle exec rails db:migrate:jh to perform above demo migration, it should create jh_hats table in JH database