e2e: add ranking tests for atom boosting (#715)
This adds four cases which are exact phrases to search for.
"assets are not configured for this binary" finds the correct document,
but it isn't shown in the summary. Our target rank doesn't capture that
this could be better, but I will use the golden file to see if I improve
this.
"sourcegraph/server docker image build" is an example of an exact phrase
which also happens to contain words of highly ranked symbols. This leads
to the exact phrase getting buried. I want to see if I can boost that.
"bufio flush writer" should find the symbol bufioFlushWriter.
"coverage data writer" should find the symbol CoverageDataWriter.
Test Plan: go test