Add user-defined command line parameter.

[MiyamuraMiyako]

Resubmit PR. Allow users to add additional command line parameters.

[AlbertShown]

Thank you for the PR @MiyamuraMiyako Few things need to be modified.

[mochalins]

Hey, just a heads-up since this PR has been hanging for a while; I'd love to review and get this towards a merge if possible, but any API-facing changes I have to leave for review from a core maintainer. Apologies for the delays, but if possible please leave this open and sit tight! @MiyamuraMiyako

[MiyamuraMiyako]

@mochalins Okay, no problem at all.

[hassandraga]

Thank you @MiyamuraMiyako.

[hassandraga]

Note: I did not test this feature yet.