rpcclient: Add GetBlockChainInfo

[chappjc]

This adds support for the getblockchaininfo RPC to rpcclient.

The main package's required rpcclient module version is bumped from v1.0.2 to v1.1.0.

[chappjc]

I'm not sure about the RPC server version bump, but I recall you saying that for a new command added to the rpcclient module, a minor version bump is required.

[davecgh]

The rpcserver major was already bumped to 5.0.0 due to the notification order change, which happened after the addition of getblockchaininfo, so there is no need to bump it again.

[chappjc]

Oh, right, sorry. I'll change that back.

[davecgh]

Please don't make any changes to the module versions over and above the very specific change required. In this case, it should only be modifying the main module's rpcclient version and nothing else. e.g. rpcclient/go.{mod,sum} should not be modified here.

[chappjc]

go build actually made the wire v1.2.0 change to rpcclient/go.{mod,sum}. Since it insisted on that change, I manually did the go mod tidy in rpcclient. I see now that go build only makes that change when run from the rpcclient folder (rather than from the repo root via go build ./rpcclient or go build ./.... I don't completely understand why that should be, but I will change the rpcclient mod files back.