As a software engineer
I want to add a gRPC endpoint for pointers 
So that pointers can be created, updated and retrieved using third party gRPC clients

Given pointer_controller.rs and pointer_service.rs exist
When adding pointer_handler.rs 
Then it should reflect pointer_controller.rs
And be added to a new &#39;grpc&#39; module under the root as grpc/pointer_handler.rs

Given gRPC requires protobuffer definitions
When adding pointer gRPC endpoints
Then create gRPC service definition for pointer request/response messages

Given gRPC needs to be integrated with Actix
When adding pointer gRPC endpoins
Then update lib.rs to integrate the gRPC pointer handler

Provide unit tests where applicable to grpc/pointer_handler.rs and related new code.

Implementation Notes

- Use Tonic as the gRPC libary and include in cargo.toml
- Use existing Tokio dependencies for async execution
- Review https://docs.rs/tonic/latest/tonic/ for Tonic docs for implementing gRPC with Rust
- Review https://github.com/hyperium/tonic/blob/master/examples/src/grpc-web/server.rs to understand Tonic integration
- Review https://github.com/Marlos-Rodriguez/rust-dual-grpc-http to understand Actix integration of Tonic endpoints 
- Create /grpc module in the project root to hold gRCP handlers
- Create /proto directory in the project root to hold proto definitions files
- Assume other handlers will be added in the future, following the same pattern, in /grpc directory/module
- Define From traits to perform mapping between structs, including errors (use ?)
- Use Actix Data instead of Arc 