Install manager updates with external installer

[stuffi3000]

Feature description

When updating the manager, having the option to install the downloaded apk with an external installer instead of through the manager itself.

Motivation

Microsoft InTune's company policy blocks the installation of apps from unknown sources. To work around this, Shizuku must be used together with Split Apks Installer (SAI).
Alternatively, one could implement installation through Shizuku in the manager directly.

Additional context

I'm unsure how many people are in the same situation, but all users with a split personal-professional mobile phone are usually limited when it comes to installing apps from outside the Playstore.
Shizuku allows to run the ADB API locally by connecting to the phone through wireless debugging. This bypasses the unknown sources restriction, but is arguably a bit cumbersome. The price to pay when you're also using your company phone for personal purposes I guess.
But yeah, I currently have to download the newest version of the launcher - or any other unofficial Apk that is - manually and install them with SAI.

Acknowledgements

• This request is not a duplicate of an existing issue.
• I have chosen an appropriate title.
• All requested information has been provided properly.
• The issue is solely related to the ReVanced Manager

[validcube]

This could be potentially fixed by #1414 as a workaround for now.