Allow configuring canister_args_file in dfx.json

[viviveevee]

Request by @bitdivine on the forum:

It would actually be really useful to be able to specify a file containing arguments. Why a file? Because then the arguments can be created by the build command, or modified by the user, without having to change dfx.json. Is there any chance that we can get something like a canister_args_file in dfx.json?

[alejandrade]

I would like to second this request

[viviveevee]

Importing comment from duplicate #3619:

It is convenient to store big init args in init_args.did file. Would be useful to be able to specify this file in dfx.json like this:
"init_arg": "./init_arg.did",
or
"init_arg_file": "./init_arg.did",