Add docs for runner fleet dashboard early adopters program

What does this MR do and why?

Addresses Write documentation for using CI Analytics with... (#424500 - closed)

We want to test the new Runner Fleet dashboard with a few selected self-managed clients. This MR provides the documentation on how to setup Clickhouse database and enable necessary feature flags for such tests.

This page is intentionally placed in our development section of the documentation and not the user one. The idea is to emphasize that using Clickhouse is still experimental, and we don't yet fully support it.

I also plan to record a video walking through this.

Ideally in the future this documentation should be broken into 3 separate pages:

1. Normal dashboard documentation which doesn't require Clickhouse
2. Clickhouse setup docs
3. Dashboard setup docs

But I on purpose budled it up toghether into a single page for now.

Review app: http://main-ee-135227.docs.gitlab-review.app/ee/development/runner_fleet_dashboard.html

Screenshots or screen recordings

I'm still working on this.

MR acceptance checklist

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doc/development/runner_fleet_dashboard.md

@@ -38,8 +38,7 @@ In order to be able to participate, you should:
 Follow these steps to setup ClickHouse as the GitLab data storage:
 
 1. [Run ClickHouse Cluster and configure database](#clickhouse).
-1. Configure access to this cluster. You can do that for [GitLab Linux packages](#gitlab-linux-packages)
-   or for [GitLab Helm Chart](#gitlab-helm-chart)
+1. [Configure GitLab connection to Clickhouse](#configure-gitlab-connection-to-clickhouse)
 1. [Enable a number of feature flags](#enabling-feature-flags)
 
 ### ClickHouse
@@ -129,7 +128,11 @@ To create necessary user and database objects:
     GROUP BY status, runner_type, started_at_bucket;
     ```
 
-### GitLab Linux packages
+### Configure GitLab connection to Clickhouse
+
+::Tabs
+
+:::TabTitle Linux package (Omnibus)
 
 To provide GitLab with ClickHouse credentials:
 
@@ -148,12 +151,37 @@ To provide GitLab with ClickHouse credentials:
    sudo gitlab-ctl reconfigure
    ```
 
-### GitLab Helm Chart
+:::TabTitle Helm chart (Kubernetes)
+
+TODO
+
+::EndTabs
 
 ### Enabling Feature Flags
 
+Features using Clickhouse are currently under development,
+so they are hidden behind feature flags.
+
+Follow [these instructions](../administration/feature_flags.md#how-to-enable-and-disable-features-behind-flags)
+to enable these feature flags:
+
+| Feature flag name                  | Purpose                                                                   |
+|------------------------------------|---------------------------------------------------------------------------|
+| `ci_data_ingestion_to_click_house` | Enables synchronization of new finished CI builds to Clickhouse database. |
+| `clickhouse_ci_analytics`          | Enables the "Wait time to pick a job" chart.                              |
+
 ## What's next
 
+We plan to enhance CI/CD analytics features further by adding:
+
+1. [Usage/cost analysis](https://gitlab.com/groups/gitlab-org/-/epics/11183)
+
 ## Feedback
 
-[feedback issue](https://gitlab.com/gitlab-org/gitlab/-/issues/421737)
+Please provide feedback on the [feedback issue](https://gitlab.com/gitlab-org/gitlab/-/issues/421737).
+In particular we would love to know:
+
+1. How easy/hard was it to setup GitLab to make the dashboard working?
+1. How useful do you find this new dashboard?
+1. What other information you would like to see on that dashboard?
+1. Any other related thoughts and ideas!