feat: System API method in_replicated_execution

[bogwar]

This PR adds a system API method to determine if the canister is running in replicated or non replicated mode.

[github-actions]

🤖 Here's your preview: https://phnfe-kyaaa-aaaak-qckia-cai.icp0.io/docs

[dsarlis]

Generally lgtm.

One minor comment I also mentioned to Bogdan offline is whether replicated execution is an established term in the spec. I know that most of us understand what it means but I am not sure if that would be clear to someone who's reading the spec.

[mraszyk]

whether replicated execution is an established term in the spec

there are already a few occurrence, but all seem to be added recently

[bogwar]

Generally lgtm.

One minor comment I also mentioned to Bogdan offline is whether replicated execution is an established term in the spec. I know that most of us understand what it means but I am not sure if that would be clear to someone who's reading the spec.

This was a very good point; I checked and we didn't actually introduce these terms properly so I've added a small clarification in the nomenclature section.