Update ClickHouse integration docs to guide user to enabling ClickHouse-backed features
What does this MR do and why?
After following instructions to configure a GitLab instance to connect to ClickHouse, it's not immediately apparent after running migrations how to use features that are dependent on these migrations or sync data over from Postgres to ClickHouse.
The change includes a link to enabling ClickHouse for analytics features, which will complete the setup process for things like Contribution Analytics and AI impact analytics.
In other terms, https://docs.gitlab.com/ee/integration/clickhouse.html and https://docs.gitlab.com/ee/administration/analytics.html describe the complete process to setting up a GitLab instance with ClickHouse, but we're missing a link to the final step of enabling usage of the connection which may confuse Self-Managed customers wanting to bring their own ClickHouse.
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