Use Gitlab::Redis::SharedState in Importers

What does this MR do and why?

As per #429461 (closed) we're starting to use Gitlab::Redis::SharedState for our importers.

We're using Gitlab::Redis::SharedState for writing purposes, and Gitlab::Redis::Cache for reading.

Screenshots or screen recordings

N/A

How to set up and validate locally

note: a quick way of testing locally:

1. Execute the Rails console using bin/rails console and cache certain values using methods like .write or .increment from Gitlab::Cache::Import::Caching module.
2. Verify that the values are correctly cached using Gitlab::Cache::Import::Caching.read.
3. Switch to this branch.
4. Reassure that the cached values remain unchanged.

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 #429461 (closed)