cmd, node: initialize ports with --instance

[weiihann]

Description

This PR adds a new CLI flag called --instance <value>, used to configure ports when running multiple nodes on the same machine to avoid port conflicts. This is only applicable for port, authrpc.port, discovery,port, http.port, ws.port.

The calculation of port numbers is as follows:

authrpc.port = 8551 (default) + `instance`*100 - 100
http.port = 8545 (default) - `instance` + 1
ws.port = 8546 (default) + `instance`*2 - 2
port = 30303 (default) + `instance` - 1
discovery.port = 30303 (default) + `instance` - 1

In a scenario where the user specify both --instance and the supported port list (i.e. port, authrpc.port, ...), then the ports specified will supersede the port values configured by --instance.

Example

Usage: geth --instance 2

authrpc.port = 8651
http.port = 8544
ws.port = 8548
port = 30304
discovery.port = 30304

Usage: geth --instance 2 --authrpc.port 8551

authrpc.port = 8551
http.port = 8544
ws.port = 8548
port = 30304
discovery.port = 30304

Usage: geth --instance 201

Fatal: Instance number 201 is too high, maximum is 200

Credits

This flag is inspired by reth.