Save encrypted files in binary format

Save encrypted files in binary format

Default to the more space-efficient binary encoding for newly encrypted files
instead of the traditional base64 encoding, eliminating the 33% overhead.

The new option 'encryption.use_legacy_encoding' allows to force the legacy
encoding format if needed. Files encoded in the old format remain readable.

Based on https://github.com/owncloud/encryption/pull/224 and
https://github.com/owncloud/core/pull/38249 by karakayasemi.

Signed-off-by: plumbeo <plumbeo@users.noreply.github.com>