benches: make jsonrpc crates optional

[niklasad1]

Make the dependency tree smaller with the default bench dependencies.

[dvdplm]

Doesn't this require a change to CI too, so we run the jsonrpc benches too?

[niklasad1]

Doesn't this require a change to CI too, so we run the jsonrpc benches too?

We're not running the daily benches on jsonrpc crate (hidden behind the feature flag jsonrpc-crate), why should we?
Isn't sufficient to run against it on releases?

However, it would probably be good to automate it otherwise it's easy to forget... so maybe not a bad idea do run it daily/weekly or something.