expose client error

[stevenctl]

What kind of change does this PR introduce?

Feature

What is the current behavior?

There is no way to see error caused by methods such as Rpc

What is the new behavior?

Simply passing through the ClientError field on the postrest client

Additional context

It might make sense to change certain method, or create variants of other methods that return (something, error) that check this so callers don't need to understand when ClientError is relevant to the specific call they want to make.

[stevenctl]

since the postgrest stuff merged i'll revert the go.mod stuff (or just bump it in this PR)? I see this project already relies on a replace onto a fork