feat(billing): Add cli subcommand for monthly active user counts

internal/proto/controller/api/services/v1/billing_service.proto

@@ -7,7 +7,6 @@ package controller.api.services.v1;
 
 import "controller/api/resources/billing/v1/billing.proto";
 import "google/api/annotations.proto";
-import "google/protobuf/timestamp.proto";
 import "protoc-gen-openapiv2/options/annotations.proto";
 
 option go_package = "github.com/hashicorp/boundary/internal/gen/controller/api/services;services";