Add native sapphire-localnet docker image for Mac

[matevz]

We're having an increasing number of developers running MacOS. Having native sapphire-localnet would be really handy. This also makes the overall codebase more stable and future-proof.

This requires:

• native oasis-node running on MacOS
• native oasis-web3-gateway
• native sapphire (and emerald) ParaTimes
• native Oasis CLI
• register new docker platform
• update the docs and remove --platform flag

Related oasisprotocol/oasis-web3-gateway#592

[aefhm]

Running sapphire-localnet on Docker MacOS under Docker VMM works directly albeit with a warning.

xi@milan oasis-web3-gateway % docker run -it -p8545:8545 -p8546:8546 ghcr.io/oasisprotocol/sapphire-localnet      
WARNING: The requested image's platform (linux/amd64) does not match the detected host platform (linux/arm64/v8) and no specific platform was requested
sapphire-localnet 2024-12-02-git920018f (oasis-core: 24.3, sapphire-paratime: 0.9.0-testnet, oasis-web3-gateway: 5.1.0)

 * No ROFLs detected.