Add Sharepoint support in Android app

### Please agree to the following

- [X] I have searched [existing issues](https://github.com/cryptomator/android/issues?q=) for duplicates
- [X] I agree to follow this project's [Code of Conduct](https://github.com/cryptomator/android/blob/develop/.github/CODE_OF_CONDUCT.md)

### Summary

Add support for Sharepoint

### Motivation

In the business environment, MS Sharepoint is a common platform to store documents / project files. Currently it's not possible to add a vault located in a Sharepoint document library, but only from OneDrive.

### Considered Alternatives

None.

### Anything else?

_No response_