Add API Error Handler (#74)

* Add error handler that converts from rpc.Status errors to Watchtower API errors.

* Better testing for ErrorHandler.

* Rename testcase and remove empty default switch case.

* Change the error status back to int64.

* Converting everything to int32s.

jsonpb wraps int64s as a string which we dont like.  We'll figure out how to use values larger than int64s when it comes up.

* Remove special casing for TraceId which isn't needed anymore.

* Removing wrappers from error details since we never need to know when they are set or unset from the end user.

* Using the helper error functions inside the project service.

* Correct usage of hclog, replace panic with Error log.

* Adding periods to all API returned errors, correct spelling, fix missed invalid argument error not using helper function.

* Change our logged errors to Error instead of Warn.

* Add TODO for defining and using our own defined API error codes.

* Add TODO to remove internal error messages.

internal/servers/controller/handler.go

@@ -15,6 +15,7 @@ import (
 	"github.com/hashicorp/watchtower/api"
 	"github.com/hashicorp/watchtower/globals"
 	"github.com/hashicorp/watchtower/internal/gen/controller/api/services"
+	"github.com/hashicorp/watchtower/internal/servers/controller/handlers"
 	"github.com/hashicorp/watchtower/internal/servers/controller/handlers/host_catalogs"
 	"github.com/hashicorp/watchtower/internal/servers/controller/handlers/host_sets"
 	"github.com/hashicorp/watchtower/internal/servers/controller/handlers/hosts"
@@ -57,7 +58,7 @@ func handleGrpcGateway(c *Controller) http.Handler {
 	// Register*ServiceHandlerServer methods ignore the passed in ctx.  Using the baseContext now just in case this changes
 	// in the future, at which point we'll want to be using the baseContext.
 	ctx := c.baseContext
-	mux := runtime.NewServeMux()
+	mux := runtime.NewServeMux(runtime.WithProtoErrorHandler(handlers.ErrorHandler(c.logger)))
 	services.RegisterHostCatalogServiceHandlerServer(ctx, mux, &host_catalogs.Service{})
 	services.RegisterHostSetServiceHandlerServer(ctx, mux, &host_sets.Service{})
 	services.RegisterHostServiceHandlerServer(ctx, mux, &hosts.Service{})