Automate gas cost comparison script to run in GH actions

[jacque006]

Depends on #138

After #138 is merged, add a Github Actions pipeline for automatically running and uploading the gas cost comparisons on contract changes so people can see the gas differences when using BLS wallets.

Considerations

• Probably need to create a markdown template to inject measurement results into.
• Run tests on any commit where ./contracts is changed.
• Use Arbitrum Testnet to run tests by default, but see if it is possible to setup and run a local node instead as it will reduce the amount of time to run the script and not require constant funding of the address on testnet.
• Upload the report to somewhere and link on the main README.md file to the latest run for main branch. This could be uploaded to somewhere on Github, IFPS, AWS S3, etc.