[New Feature]: Migrate to SHA3-256

Description of the new feature/enhancement

Instead of SHA2, it would be forward looking to start using SHA3 for everything from the indexed manifest locations to having it available as an option instead of SHA2 for the installer checksum

Proposed technical implementation details (optional)

1. Update the index creation to use SHA3 and republish with a new index
2. Add a new manifest field for installer SHA3-256, and update logic to require either the SHA256 or SHA3-256, and enlighten the client to use whichever algorithm is appropriate
3. Update Icons to use SHA3-256
4. Add new manifest field for FileSha3-256
5. Add new manifest field for SignatureSha3-256
6. Update Manifest Creation Tools to use SHA3 instead of SHA2

This could probably be separated into several sub-issues for wherever SHA2 hashes are currently used across the product, as I'm sure each portion will require a slightly different approach or implementation

Start by mapping the SHA2 uses named in the issue: index creation, installer checksums, icons, manifest fields, signatures, and manifest creation tools. Determine whether these areas should become separate sub-issues; done would require an agreed scope and corresponding client, manifest, index, and tooling changes.