runtime/src/enclave_rpc: Simplify RPC context

[peternose]

Trying to remove cloning of identity, consensus verifier and other data for every RPC request and just pass all these parameters in a constructor. The final code should look like this:

// Init all components.
let secrets = Secrets::new(identity, consensus_verifier, ...);
let churp = Churp::new(identity, consensus_verifier, ...);

// Register methods.
rpc_dispatcher.add_methods(secrets.methods());
rpc_dispatcher.add_methods(churp.methods());

fn secure_rpc_method(&self, ctx: &RpcContext, req: &Request) ->  Result<Response>
fn insecure_rpc_method(&self, req: &Request) ->  Result<Response>
fn local_rpc_method(&self, req: &Request) ->  Result<Response>

Open for suggestions and improvements.

Thinking out loud: In the future, we could also consider refactoring runtime startup via start_runtime, splitting it into two parts: initialization and start. The first method could return a new struct Runtime, which would provide access to identity, consensus verifier, RPC dispatcher, protocol, etc., to other methods, such as the key manager initialization method. This approach
could eliminate the need for PreInitState and PostInitState, and maybe allow us to have non-static variables in the key manager.

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (00e2494) 66.26% compared to head (0fcf9c9) 66.29%.
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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5555      +/-   ##
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+ Coverage   66.26%   66.29%   +0.02%     
==========================================
  Files         546      546              
  Lines       56861    56861              
==========================================
+ Hits        37679    37694      +15     
+ Misses      14740    14738       -2     
+ Partials     4442     4429      -13     

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