Add command line parameter for silent installations to disable NVDA at the logon screen and enhance portable-path command line behavior (PR #8623)
Fixes #8574
### Summary of the issue:
1. In the current situation, it is not possible to specify the start at logon behaviour from the command line. This issue is relevant for system administrators who want to install NVDA silently on a multi user system.
2. When starting NVDA with the `--portable-path` command line parameter and creating a portable copy from the GUI, the provided portable path isn't shown in the gui as one might expect.
### Description of how this pull request fixes the issue:
1. Added a `--enable-start-on-logon` command line parameter. It should be specified as `--enable-start-on-logon=True` or `--enable-start-on-logon=False`, just `--enable-start-on-logon` will show an error message. Alternative supported values are `yes/no`, `on/off`, `1/0` (i.e. this option behaves as `configobj boolean`). NVDA's behaviour is to default this to `True`
2. When the `--portable-path` parameter is provided at NVDA start, the provided path is now pre-filled in in the portable copy creation dialog.