Application level error consumption and handling

[EverlastingBugstopper]

fixes #146

This PR establishes patterns for application-level error handling in Rover by creating the rover::error module. This module exports Result<T, RoverError>, which is used in Rover to exit the application with the proper status code. RoverError is a struct that wraps anyhow::Error and provides contextual information about the error in enums Option<Code> (error codes) and Option<Suggestion> (possible solutions that helps the user troubleshoot). These are wrapped up into a Metadata struct, which can be created from an anyhow::Error. RoverError also has a Display implementation that is used in Rover to display the errors any way we like. I've taken a shot at a default Display implementation here, but I'm very happy to work out the exact details on how it looks like with y'all.

here's an example of an error with a solution:

$ rover config profile show
error: No non-sensitive config found for profile "default"
        Try re-running this command with the '--sensitive' argument

once we add error codes, they will look something like this:

$ rover config profile show
error[E210]: No non-sensitive config found for profile "default"
              Try re-running this command with the '--sensitive' argument

In RoverError's constructor, Code and Solution are created by taking advantage of anyhow::Error::downcast. This allows us to find the underlying Error enum exported by various crates (like houston::HoustonProblem and rover_client::RoverClientError). Here, we can determine the error codes and solutions for various errors with match statements on those library-provided error enums!

I'm hoping this allows us to take a bit of an incremental approach to improving errors, as we see areas for improvement, we can extend our library error types, and adjust their solutions/error codes in rover::error::metadata.

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Let's merge this as is if it all looks good and then we can take care of improving individual errors and adding codes/suggestions incrementally.

[lrlna]

If you like, let's pair on this!

[lrlna]

This looks really good, @EverlastingBugstopper. Merge merge merge away!