updatecheck: include aggregated repository statistics in pings

Created by: keegancsmith

We want to start including the number of lines of code indexed by Sourcegraph as well as the total size of all git repositories stored on Sourcegraph.

This commit was created by copying the structure of the saved searches pings commit.

Depends on https://github.com/sourcegraph/sourcegraph/pull/13763

Fixes https://github.com/sourcegraph/sourcegraph/issues/13713