Write documentation for using CI Analytics with ClickHouse for alpha-users on self-managed

We want to test the new CI Analytics with ClickHouse with a few users on self-managed.

Setting up this feature won't be easy:

1. They will need to set-up clickhouse instance
2. Setup credentials
3. Enable a few feature flags

We need to document all of that in some sort guide.

This documentation should be under "Development" section, not in our normal docs:

Please see https://docs.gitlab.com/ee/architecture/blueprints/clickhouse_usage/#non-goals and https://docs.gitlab.com/ee/architecture/blueprints/clickhouse_usage/self_managed_costs_and_requirements/index.html for more details. Documentation for self-managed might be interpreted as the feature is supported for self-managed, which is not the case at the moment. So if there will be docs they should be stating that it's development facing only or experimental.