Blob view: revision selector is slow

[camdencheek]

When first used, the revision selector takes a second or two to load. We should look into whether we can speed this up or preload it (depending on how frequently it's used).

[camdencheek]

Looked into this a bit and found that, for each reference, we're making a followup git request to resolve the author information.

We looked into two ideas:

1. use git for-each-ref to return a formatted list with all the authorship information in one go
2. batch resolve the authorship information

The problem with both is we don't know in advance whether the authorship information is needed, and our GraphQL library doesn't support inspecting which fields are requested.

[camdencheek]

cc @fkling since we chatted briefly about why this is slow on the backend

[camdencheek]

Closing since we don't plan to do any additional work here