Option to ignore existing installed products

[CiaranMcAndrew1]

It is useful to call mpm to add new packages to an existing installation. This has a lot of uses in container workflows and CI systems.

However, if the user requests packages that are already installed, mpm will return an error. e.g.

Error: Unable to install these products because they are already installed:
MATLAB
MPM Installation Failure. See below for more information:
(Feb 26, 2024 14:00:33) Starting download of product meta data
(Feb 26, 2024 14:00:33) Finished downloading product meta data
(Feb 26, 2024 14:00:38) Starting to retrieve support package metadata
(Feb 26, 2024 14:00:42) Finished retrieving support package metadata
(Feb 26, 2024 14:00:47) The following products are already installed and will not be updated: MATLAB

This means the caller needs knowledge of what is already installed, or to somehow get that information from another source first.

Instead, it would be very useful to have a command line argument to suppress this error, such as --ignore-installed-packages.