feat: Implement aws kms signer support for deploys

[shark0der]

Context

Use AWS KMS to deploy contracts.

Changes proposed in this pull request

This PR adds @nexusmutual/ethers-v5-aws-kms-signer as a dep and uses it for the deployer script.

Test plan

Currently it was ran manually to perform a self-tx on mainnet.

Checklist

• Rebased the base branch
• Attached corresponding Github issue
• Prefixed the name with the type of change (i.e. feat, chore, test)
• Performed a self-review of my own code
• Followed the style guidelines of this project
• Made corresponding changes to the documentation
• Didn't generate new warnings
• Didn't generate failures on existing tests
• Added tests that prove my fix is effective or that my feature works

Review

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• 🚀 = Feedback