Add client build sha to rollbars

[StachuDotNet]

Knowing which sha the build is on may assist in quickly knowing whether a Rollbar was before or after some deploy.

We already have that info in the client globals, so shouldn't be too difficult to do.

[StachuDotNet]

if rollbar could somehow dynamically compare such against the 'current sha' and display that as a column, would be bonus cool.

[pbiggar]

I think this is done?

[StachuDotNet]

Yeah, thanks for the reminder https://github.com/darklang/dark/pull/4645