frame-session: Introduce a proper proof of key ownership

[bkchr]

frame_session::set_keys supports providing a proof as second parameter. This proof was not yet checked. This pull request introduces a verification of this proof and also a way of generating this proof. The proof in FRAME are concatenated Signatures. These Signatures are in the same order as the public keys in the SessionKeys struct. Each signature is signing the owner, proofing that the generating party has access over the private key associated to the public session key. The owner in FRAME is the account id of the account that will call set_keys, aka the account of the validator.

This pull request is changing the SessionKeys runtime api. This still requires a RFC, as this is a public interface of the Polkadot runtime.

@jacogr polkadot-js should provide a way to use the runtime api directly to generate the sessions keys.
@paritytech/docs-audit this will require updates of the validator documentation to tell them what to pass for owner and that they need to pass proof to set_keys.

[bkchr]

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[bkchr]

@jacogr polkadot-js should provide a way to use the runtime api directly to generate the sessions keys.

Scrape that, we need a new RPC for this.

[kianenigma]

https://github.com/orgs/paritytech/teams/docs-audit this will require updates of the validator documentation to tell them what to pass for owner and that they need to pass proof to set_keys.

This is mostly in the Polkadot wiki, I will ping the w3f folks and also setup a system where they can listen to mentioned of this docs-audit team. But all in all, you should do your best to update the docs around this in the rust docs of pallet session at first.

[paritytech-cicd-pr]

The CI pipeline was cancelled due to failure one of the required jobs.
Job name: test-linux-stable 3/3
Logs: https://gitlab.parity.io/parity/mirrors/polkadot-sdk/-/jobs/3943056