Files metadata endpoint

[PVince81]

@DeepDiver1975 @butonic as discussed at the conference:

"/meta/$fileid" DAV and View endpoints to access versions, etc.

[DeepDiver1975]

DAV @sharidas :

• create MetaData collection in dav app - name 'meta'
• second path is the file id (uuid encoded bigint)
• create subfolder v for versions
• create subfolder p for previews

Filesystem @DeepDiver1975:

• create mount 'meta' and corresponding storage implementation
• define storage interfaces for versions etc

Frontend:

• use v dav endpoint in versions sidebar
• use p dav endpoint to generate previews

[DeepDiver1975]

@Peter-Prochaska

Test Scenarios:

• restore version of read only shared file -> shall not be allowed