[fastx CLI] Add customisation to genesis

[patrickkuo]

As per GDC Eng Deliverables doc

fastx start –genesis <some_config_file> can be used to do the above with a different genesis state (e.g., preloading modules and NFT’s, as some of the demos we are building will require). This config file needs to be able to encode arbitrary Move structs (i.e., not just gas coins) in order to support the preloading NFT’s requirement

The current implementation hard coded the genesis to create 4 authorities, 5 account with 5 gas object each, we need to support genesis customisation using config file.