Allow users to define their own extension for advanced tracking.

Describe your suggested feature

Since the first implementation of advanced tracking, aka Komga, Kivita and Suwayomi, the extensions required use them has been hard coded into the app with getAcceptedSources (example). Previously, having these extensions hard-coded made sense as they where officially maintained by Tachi, however since both Tachi this fork (Mihon) won't be maintaining extension anymore, including those for self-hosting, it would make more sense to let the users select a extension and define it as the extension to use for "this" advanced tracking. The extension would then provide upon asked for the saved credentials. This would allow users to make their own customized extension for their self-hosted server and still keep the tracking functionality without needing to have the right name eu.kanade.tachiyomi.extension.all.* as having the same name multiples time can sometimes cause conflicts.

Would also fix the following issues : https://github.com/mihonapp/mihon/issues/55

Other details

I think this feature would goes with the new direction of bringing our own content.

Acknowledgements

[X] I have searched the existing issues and this is a new ticket, NOT a duplicate or related to another open or closed issue.
[X] I have written a short but informative title.
[X] I have updated the app to version 0.16.3.
[X] I will fill out all of the requested information in this form.

mihonapp / mihon