Use memguard for secrets

[jfantinhardesty]

What type of Pull Request is this? (check all applicable)

• [x] Refactor
• [ ] Feature
• [ ] Bug Fix
• [x] Optimization
• [ ] Documentation Update

Describe your changes in brief

Use memguard to store secrets, passphrases to prevent heap inspection attack. Now passphrases are stored in a memguard enclave and only retrieved immediately before they are used. This includes s3storage, azstorage, and using a passphrase to secure a config file.

Checklist

• [x] Tested locally
• [ ] Added new dependencies
• [ ] Updated documentation
• [ ] Added tests

Related Issues

• Related Issue #
• Closes #