Add metric to count bulk import entities states

What does this MR do and why?

Add metrics to count bulk import entities by the state: Finished, Failed, Timeout

Related to: #341506 (closed)

How to set up and validate locally

1. In Rails console, run ServicePing::SubmitService.new.execute
2. Then check the metrics using the commands:

RawUsageData.last.payload['usage_activity_by_stage_monthly']['manage']['project_imports']

RawUsageData.last.payload['usage_activity_by_stage_monthly']['manage']['group_imports']

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.