0.20.0-icsystemtest.1: feat: init_arg_file in dfx.json (#3721)

* Add  support in dfx.json. (WIP)

* Trim the string read from the arg file.

* Update dfx-json-schema.json file.

* Get the absolute path of 'init_arg_file', and update changelog.

* Fix cargo format.

* simplify a bit

* comments

* improve the warning message

* changelog

* fmt

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Co-authored-by: Vincent Zhang <zhangwei983@hotmail.com>
Co-authored-by: Linwei Shang <linwei.shang@dfinity.org>