Add errorCb to server interceptors and update readme

[Robin-Hoodie]

No description provided.

[zoltrain]

Hello!

First of thanks for the PR, we're no longer using this internally hence why it's been quiet. I thought grpc-node would've added interceptors by now but it seems an API hasn't even been discussed yet. grpc/grpc-node#419 This PR looks good but @Robin-Hoodie would it be possible to add a test to make sure it's being called on error?

[Robin-Hoodie]

Hey @zoltrain , I created this PR a long time ago and don't remember a lot of the code.

As you're no longer using this internally, can I ask what you're using instead?

[zoltrain]

@Robin-Hoodie We've moved over to Go, and the official grpc module which has support for interceptors. It's not that this isn't useful in node world, it's just not something we use everyday anymore. It was the fact that node lacked support that we created this in the first place, we found good observability is hard with out this type of pattern.