Add ability to choose discord APK file to patch, from alternative sources

[Rairof]

Add the ability to choose the discord .apk file manually from internal storage similar to revanced manager. Helps with users who might have issues with fetching default APK files from the manager automatically even after trying out all available proxies, and then wanting to just select their discord apk file they downloaded from other sources within vendetta manager or just use their desired source link for discord APK into the manager app for it to patch.
A pretty crude concept picture-