Clarify default configuration options for the sandbox

[heidihoward]

It might be useful to highlight in the docs where different default configurations options are used by sandbox.sh.

For instance, the documentation for the sig delay says this is 1s/1000ms, but in e2e_args.py (which is used by sandbox.sh and most of our e2e tests), we actually specify a default of 100ms.

[achamayou]

Yes, the sandbox is a thin wrapper around some of the test infra, and so tends to share its defaults. That makes sense much of the time, but not always. In tests we want lower commit latency (shorter CI time), at the expense of throughput and ledger size, but that's not necessarily true for the sandbox.

I think a simple way to think about this is that the sandbox should never override a cchost default. If we think it's a good generic default, it's a good default for the sandbox.

[achamayou]

A relatively cheap and easy improvement is to define a mapping of CLI options to JSON paths in the config schema. That can be used automatically to look up the default and the description, ensuring they stay in sync.