Add JSONLinesCache to write cache entries to stdout
Created by: mrnugget
This is part of https://github.com/sourcegraph/sourcegraph/issues/26929
and requires https://github.com/sourcegraph/sourcegraph/pull/27061 on
the sourcegraph/sourcegraph
side.
It adds a JSONLinesCache
that writes cache entries to stdout. It's
used when executing src batch exec
, which results in cache entries
being transfered to the Sourcegraph server via the executor.