Filter search to repos containing another search term

Created by: dadlerj

Describe the feature request.

Run a search, filtered to only repos that also have results for an initial search

Is your feature request related to a problem? Please describe.

A user would like to:

• Search for a word X, but;
• Only in repos that also have results for the word Y

Describe alternatives you've considered.

Execute two separate searches:

• First, using the Sourcegraph API to find repos containing X, such as this search on Sourcegraph.com's API console
• Second, using the Sourcegraph API constrained by the search filter repo:(r1|r2|...) where r1, r2, and ... are repos found in the first search

Additional context

Refer to full API access documentation at https://about.sourcegraph.com/docs/features/api