Improve the message that appears in the UI when there are problems with repos in a code host

Created by: mike-r-mclaughlin

Feedback

A warning icon appears in the upper right corner of the UI for site admins when there are problems syncing repositories from a code host.

Example:

It is always a generic (and sometimes misleading) message: "Can't connect to <the code host name>"

This can cause a lot of confusion and lost time when there is actually no problem connecting to a code host but rather there is a problem with a single (or a subset of) repository contained in the code host. For example, if the token does not have access to a single repository, this message appears. There is no problem connecting to the code host. In fact, there's not a problem with all of the repositories except 1 in this example. If you remove/exclude the failing repo, this message goes away.

Customer

https://github.com/sourcegraph/accounts/issues/3

/cc @jplahn @ryphil