refactor(engine): redesign the Retrieval service (#375)

Description

• redefine public interface of the data retrieval service
• parse jobs into target groups
• add new retrieval states (renewed and snapshotting) to describe a new refresh model
• configure jobs depending on filesystem manager and detach them to run independently
• prepare a basis for jobs validation system
• combine calls of all available jobs using RefreshData() and SnapshotData()

Related issue

#375 (closed)

Examples

Retrieval's public methods

Run(ctx context.Context) error
Reload(ctx context.Context, retrievalCfg *config.Config)
RefreshData(ctx context.Context, poolName string) error
SnapshotData(ctx context.Context, poolName string) error
Stop() 
ReportState() telemetry.Restore

Checklist

• MR description has been reviewed
• MR changes are functionally tested
• MR does NOT have text changes OR there are text changes and they have been reviewed
• MR does NOT have API/CLI changes OR there are API/CLI changes and they have been reviewed
• MR does NOT have UI changes OR there are UI changes and they have been reviewed

Closes #375 (closed)