Add section about additional command-line arguments to Step Development Guidelines

[Bence1001]

Context

• Many steps run as a wrapper around specific command-line tools, such as xcodebuild.
• Although steps try to provide inputs for managing most arguments of those tools for ease of use, this is not always the case.
• Therefore, providing additional command-line arguments should always be possible via a dedicated step input (e.g. via xcodebuild_options in case of Xcode Archive).
• Steps should follow this as a best practice.

Changes

• Added a section about additional command-line arguments to Step Development Guidelines.