Call v7 commands in `plugin.CliConnection`

What's the user value of this feature request?
CF CLI plugin developers will have use of the v7 commands programmatically.

Who is the functionality for?
All CF CLI plugin developers.

How often will this functionality be used by the user?
Every user-developed plugin will use it.

Who else is affected by the change?
It will cause plugins depending on v6 specific options to commands like push to break when calling CliCommand(args...).
Otherwise, it shouldn't affect users.

Is your feature request related to a problem? Please describe.
During recent development of a CF CLI plugin, I ran into a problem when trying to use push with a manifest that had buildpacks in it. The error was that buildpacks wasn't supported in legacy push.

Describe the solution you'd like
I would like for the CliConnection to call the commands of the CF CLI I have installed (v7.2), rather than the legacy commands.

Describe alternatives you've considered
Currently, the alternative I am working with is calling cf7 push programmatically with exec.Command. I acknowledge this as a workaround, not a real solution. That's why I am opening this feature request.

Additional context
This is the first CF CLI feature request I've opened, so any feedback is welcome.

Note:
As of the GA of the v7 CLI, the v6 line is no longer under active development and will be updated only to patch CVEs or fix severe blocking defects with no workarounds.