20750/20927: Add TODO about network error handling

20750/20927: Add TODO about network error handling

The commit message for 9717f88d29310067fa70e19fb9afb3679c036bc4 says:

> This may also provide better behavior in cases of network hiccups or
> other remote server turbulence.

This was written with the expectation that those problems would raise
`HTTPClient::BadResponseError`. That was mistaken. Those problems
actually raise lower-level socket exceptions instead.

We now have a ticket to improve the error handling here. It's out of
scope for #20750, since the error handling is no worse than it was
before the branch.

Arvados-DCO-1.1-Signed-off-by: Brett Smith <brett.smith@curii.com>