feat: GitHub Actions improvements (auto-release, better tests)

[smallstepman]

• Additional check if assets.did file has the same content as the upstream one https://github.com/dfinity/cdk-rs/blob/main/src/ic-certified-assets/assets.did
• Automatic releases when pushing to main (example)

[smallstepman]

Check and Test is supposed to fail until this #31 is merged

[smallstepman]

I took another stab at it:

• split candid check into separate yml
• use actions-rs/toolchain instead of manually installing rust toolchain (uses rust-toolchain.toml) (had to use forked version, let me know if how big of a no-no this is from security standpoint. I already emailed the author of actions-rs/toolchain asking to add more maintainers to the project)
• make release workflow run only on merged pull request to main banch
• split dfx install and wasm tasks in release workflow
• shave few tasks from release workflow
• use rust toolchain version from rust-toolchain.toml for workflow caching actions/cache

[smallstepman]

Thanks!

I've never set up branch protection rules myself, so I don't have a well-established feeling for how it works or what's the good naming convention or which candidates are a good pick for :required, so for now I'm just going to follow your suggestion to see how this plays out, but overall the idea looks sweet, tl;dr many thanks for suggestion:D.

Done