[4.0] Added snapshot to-json subcommand to leap-util

[vladtr]

This PR adds the following subcommand:

 bin/leap-util snapshot to-json --help
Convert snapshot file to json format
Usage: bin/leap-util snapshot to-json [OPTIONS]

Options:
  -h,--help              Print this help message and exit
  --help-all             Show all help
  -i,--input-file TEXT REQUIRED
                         Snapshot file to convert to json format, writes to <file>.json if output file not specified (tmp state dir used).
  -o,--output-file TEXT  The file to write the output to (absolute or relative path).  If not specified then output is to <input-file>.json.
  --chain-id TEXT        Specify a chain id in case it is not included in a snapshot or you want to override it.
  --db-size UINT [65536] 
                         Maximum size (in MiB) of the chain state database

[heifner]

Please update the PR description with the latest options.