feat(dav): allow uploading folders to public shares

[skjnldsv]

Fix #15921

Explanations

Because we cannot give read permissions on a file drop, uploading subfolders is not possible.
Each parent will throw thus preventing to create nested paths. This allowed us to NOT touch the way the normal webdav works and keep things clean.

To circumvent this, we hijack the method in the fileDrop plugin.

1. We always return 201 when doing a MKCOL, thus faking any path being created
2. This allow the uploader to believe the path leading to a file exists
3. Then it allows us to create said path before handling the conflicts as we used to do.

Details

• We do not handle folders conflicts. If a folder already exists, uploading files will merge folders together
• We force the declaration of a Nickname header if you wanna upload folders. This is to make the file tree clean and help share owners knowing who uploaded a file

Secondary

Also includes the removal of a piece of code that was creating issues in the plugin bootstrapping: aa41532
The getHTTPMethods is only here to declare new methods that aren't already handled by the dav server. It is not to conditionally enable or disable a plugin.
https://github.com/nextcloud/3rdparty/blob/1a2d791504fcbbe4758e721877c640cd55a7199b/sabre/dav/lib/DAV/Server.php#L506-L530

[susnux]

🚀 Only found some casing things