Code Insights: Parallel requests in the built-in search insight fetcher

Created by: vovakulikov

In case if an insight has more than 4-5 data series and a few repos to run over we have a multiplication number of search requests (It comes from the nature of how we built our search API-based insight). We avoid a big number of network requests by our batching request but it's still too heavy for our BE to make it.

Possible solutions

1. Add some limitation for the repos field at the creation UI and by this avoid a big number of search requests.
2. Add a parallel mechanism to split requests over big number of search requests in the search-based insight fetcher.