e2e: add ranking tests for atom boosting

[keegancsmith]

This adds two 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

[keegancsmith]

I feel like there are many more examples which weren't just about exact phrases, but had more to do with tie breaking. Do you remember what those examples were? I wanna get a set of decent examples to help guide the work, but what those were in my brain have ended up the same place as all my christmas wrapping.

[stefanhengl]

Any query that contains terms that are highly ranked individually should do.

Example:
r:golang/go bufio flush writer

There is a bufioFlushWriter but we don't find it. I believe if we added the atom scores it should surface. If we accounted for term proximity even more.

Example:
r:golang/go coverage data writer

This is very similar but even more extreme. The top match right now has "coverage" and "data" just in comments. The best match is not on the first page (symbol CoverageDataWriter)

[keegancsmith]

@stefanhengl thanks those are some good test cases that we do poorly at. Added them.