Extended and more easy support for external shares

[Mannshoch]

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Is your feature request related to a problem? Please describe.
The most annoying but also promising tool is the possibility to add external shares.

At moment, I get several shares to some cloud storeage which content that gets updated frequently. Most of these shares do not need a username and password.

Describe the solution you'd like
Replace the UI and follow an analytic way.

1. User could somewhere add any Link he get and tick “Analyse”
2. User could (not required) add username and password to allow analyse behind a login form.
3. Nextcloud check the URL for hints to several protocols.
   1. check if a .well-known exist
   2. check redirects
   3. check content
   4. check for login-forms or password less access
4. ask for username/password if not already provided or password less
   7, ask what integration in Nextcloud is wished if more than one is detected and possible.
   • e.g. ohter Nextclouds provide contact, calendar, files, etc. may not all integration is wished.
   • e.g. file acces is not needed but integration in Photo.

• Allow addons to add own protocol, add detection rules and integration if certain requirement are given.
• add a generic html reader. e.g. If I get a shortlink for some thirdparty cloudstorage (without support for a known way) with a image/file galery. It would be nice if Nextcloud would be able to extract the images and files from html and allow me access them over a nextcloud directory.

Additional context
Issues that could be solved along this approach: #35274
Blueprint: https://help.nextcloud.com/t//232809