Add sign and signature verification tool

What's Changed

• add sign tool by @shrimalmadhur in https://github.com/coinbase/rosetta-cli/pull/386
• Add signature verification tool in rosetta-cli by @shrimalmadhur in https://github.com/coinbase/rosetta-cli/pull/387
• add key generate command by @shrimalmadhur in https://github.com/coinbase/rosetta-cli/pull/388
• update rosetta-skd-go to 0.8.3 by @jingweicb in https://github.com/coinbase/rosetta-cli/pull/389

Full Changelog: https://github.com/coinbase/rosetta-cli/compare/v0.10.2...v0.10.3