Add option in viewer to directly show a plugin page
Testing Done:
Ran `gplugin-gtk4-viewer -p gplugin/native-basic-plugin` and it opened the `basic plugin (C)` page directly.
Ran `gplugin-gtk4-viewer -p asfalskjf` and it exited with an error.
Reviewed at https://reviews.imfreedom.org/r/2148/
ifnotget_option('install-gplugin-gtk4-viewer')
summary('gplugin-gtk4-viewer',
'You have disabled installation of gplugin-gtk4-viewer which is a '+