cargo build should build icx-asset

[jplevyak]

Do we want to build icx-asset by default from the root directory? It isn't happening currently.

[sesi200]

@smallstepman what do you think?

[jplevyak]

For context, my template for Rust projects is to include the asset canister functionality into a single Rust backend and then use icx-asset to sync the assets as part of the deploy workflow. It is cheaper and easier to manage than having a separate asset canister. As an aside it would be nice if icx-asset could use the default dfx identity for the pem file for this workflow, but I work around that with a makefile.