Replace gRPC Backend (#10)

**Rationale:**

Having two separate servers and communication methods resulted in additional maintenance & the need to convert often between backend & frontend data types.
By moving the backend communication off of gRPC and to just use websockets it both gives more control & allows for simplification of the implementation.

#8

**Changes:**

- Replaces gRPC backend.
  - New implementation automatically handles reconnect logic
- Implements an api layer
- Migrates examples to the api layer
- Implements a proc macro to make command handling easier
- Implements unit tests for the api layer (90+% coverage)
- Implements integration tests for the proc macro (90+% coverage)

Reviewed-on: #10
Co-authored-by: Sergey Savelyev <sergeysav.nn@gmail.com>
Co-committed-by: Sergey Savelyev <sergeysav.nn@gmail.com>

server/src/http/mod.rs

@@ -1,9 +1,11 @@
 mod api;
+mod backend;
 mod error;
 mod websocket;
 
 use crate::command::service::CommandManagementService;
 use crate::http::api::setup_api;
+use crate::http::backend::setup_backend;
 use crate::http::websocket::setup_websocket;
 use crate::panels::PanelService;
 use crate::telemetry::management_service::TelemetryManagementService;
@@ -31,6 +33,7 @@ pub async fn setup(
             .app_data(cancel_token.clone())
             .app_data(panel_service.clone())
             .app_data(command_service.clone())
+            .service(web::scope("/backend").configure(setup_backend))
             .service(web::scope("/ws").configure(setup_websocket))
             .service(web::scope("/api").configure(setup_api))
             .wrap(Logger::default())