Add Sidekiq worker to re-enable pull mirror configuration

What does this MR do and why?

Contributes to #368021 (closed)

Problem

We disable pull mirroring configuration when client downgrade their subscription. But we don't re-enable them back, in case when the subscription is extended after the downgrade.

Solution

Add a Sidekiq worker that enables previously disabled pull mirroring configurations when subscription is re-activated.

How to set up and validate locally

1. Enable feature flag Feature.enable(:add_refresh_pull_mirror_worker)
2. Setup a project with a pull mirror (see docs)
3. Mark pull mirroring as hard failed

project = Project.find(<id>)
import_state = project.import_state
import_state.set_max_retry_count
import_state.save!

puts import_state.retry_count
# 15

4. Run PullMirrors::ReenableConfigurationWorker from console

project = Project.find(<id>)
PullMirrors::ReenableConfigurationWorker.perform_async(project.namespace.id)

# wait till the job is completed

puts project.import_state.retry_count
# 0

MR acceptance checklist

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