As a software engineer
I want to add a gRPC endpoint for public scratchpads
So that public scratchpad scan be created using third party gRPC clients

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

Given gRPC requires protobuffer definitions
When adding public scratchpad gRPC endpoints
Then create gRPC service definition for public scratchpad request/response messages in /proto/public_scratchpad.proto and share Scratchpad type between /proto/private_scratchpad.proto  and /proto/public_scratchpad.proto 

Given gRPC needs to be integrated with Tonic server
When adding public scratchpad gRPC endpoins
Then update lib.rs to integrate the gRPC public_scratchpad_handler.rs

Given /grpc/private_scratchpad_handler.rs already exists
When adding the public_scratchpad_handler.rs
Then use private_scratchpad_handler.rs as an example

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

Implementation Notes

- 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
- Place any unit tests at the bottom of the same file as the associated production code
- Increment patch version of anttp package in Cargo.toml