Add ability to do contract verification

[krebernisak]

There is no Etherscan on Solana that we could use to publicly verify deployed contracts, but maybe we could add a public helper script using Anchor Verifiable Builds so users could verify themselves, or CI could do it for them and report it.

Resources:

• No easy way to verify source of on-chain programs solana-labs/solana#12232
• https://project-serum.github.io/anchor/getting-started/verification.html#building

[archseer]

We weren't able to use anchor build --verify on the CI because it expects to spawn it's own Docker container, but it's already running in a container. It ends up building nothing and just failing. I think the environment is deterministic enough though (since we're building inside projectserum/build, which is what --verifiable does), we just need to validate if the sha256 matches a local anchor build --verifiable output.