Draft: Use application settings product_analytics_data_collector_host

What does this MR do and why?

NOTE: This MR will be merged only after backfill migration is run in production.

Application settings jitsu_host and collector_host should be stored separately. However, currently we only store jitsu_host and calculate the collector_host based on jitsu_host.

Recently, we added a new product_analytics_data_collector_host to application_settings table to store the above-mentioned collector host. We're backfilling the values with a post-migration.

This current MR is implementing using of product_analytics_data_collector_host instead of regex replace.

Screenshots or screen recordings

No changes.

How to set up and validate locally

1. Visit http://gdk.test:3000/gitlab-org/gitlab-shell/-/product_analytics/dashboards/setup
2. You should see a sdk host text field
3. In rails console, update product_analytics_data_collector_host column to another url
4. Refresh the page. You should see the new url in the sdk host field

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #389490 (closed)