Ignore the jsonrequestobject argument to the getblocktemplate RPC

[teor2345]

Motivation

Our stub getblocktemplate RPC will fail if it gets any arguments.

But we want to ignore the optional jsonrequestobject argument instead, because we're not going to support any optional features requested by clients.

Specifications

https://zcash.github.io/rpc/getblocktemplate.html

Designs

Accept an Option argument and ignore it.

Related Work

If we discover that clients need optional features, we can parse the argument and implement them later.

[arya2]

Accept an Option<String> argument and ignore it? Does that work?

It seemed to cause ParseErrors for the JsonParameterObject in submitblock when that was called with only one parameter.

Update: I was wrong, jsonrpc handles Option<T> params as expected, so the design in this ticket would work.

[teor2345]

Accept an Option<String> argument and ignore it? Does that work?

It seemed to cause ParseErrors for the JsonParameterObject in submitblock when that was called with only one parameter.

I'm not exactly sure how the jsonrpc library argument processing works, but unlike submitblock, getblocktemplate doesn't need any arguments at all.