feat: Support features setting for reproducible builds

[frol]

There are use-cases where users want to specify feature flags to compile contracts for different environments, e.g. testnet vs mainnet

[dj8yfo]

This could be done. Alternatively, one could use https://doc.rust-lang.org/cargo/reference/build-scripts.html#rustc-cfg in build script depending on a value from passed_env in manifest, but this says it only offers limited support of features (not enabling optional dependencies and sub-features, as far as i've understood), so just appending value from --features would be a simpler/more complete way to do this.

[dj8yfo]

The --features flag of non-reproducible command may be made repeatable with vec_multiple_opt interactive clap option to better mirror behaviour of plain cargo command

[frol]

I don't understand how to use build-scripts when I just want to build a simple contract.

[dj8yfo]

I don't understand

Well, that was me exploring a variant of containing all build parameters, not defined in source code, to passed_env. But that would be more complex and not support features completely, so just re-adding previously removed --features flag will be simple.
Doing this once per flag when needed makes more sense than just bulk adding a lot of options with no specific purpose in mind