Add metadata section "icp:public git_commit_id" to canister wasms

[aterga]

This PR is a suggestion for adding a metadata section that marks the git_commit_id of this II canister build.

Intended usage:

On locally built canisters:

dfx canister metadata $IIC_CANISTER_ID git_commit_id
0000000000000000000000000000000000000000

On canisters built via CI:

dfx canister metadata $IIC_CANISTER_ID git_commit_id
# Outputs an actual git commit SHA that allows distinguishing canister versions via CLI

Inspired by https://sourcegraph.com/github.com/dfinity/ic/-/blob/bazel/canisters.bzl?L120

[frederikrothenberger]

Hi Arshavir

Thanks for the contribution.

Could you give a little bit of context, what this metadata section is used for (other than just being consistent with canisters from the monorepo)?

Is it a requirement, to set 0000000000000000000000000000000000000000 for locally built canisters? Because the build script already has the II_VERSION variable (that is provided to give release information in the front-end), which is "$commit,$release,$dirty". The metadata field should consistent with that.

Is it also an option to just leave the field off completely instead of filling it with bogus content for locally / dirty built canisters?

[nmattia]

Closing because this seems stale, feel free to reopen