Add Redis data source to service ping context

What does this MR do and why?

It adds redis data source implementation into Gitlab::Tracking::ServicePingContext that builds gitlab_service_ping context

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

How to set up and validate locally

This is backstage change only for now, so the only way to verify is to use specs added in this MR

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.