fix: Write memcache locking path hash to exception

[juliushaertl]

When trying to investigate stale locks it can be helpful to have the actual hash available for checking in redis. Otherwise one needs to manually construct the has from the storage and path.

Reference on the hashing:

server/lib/private/Files/Storage/Common.php

Line 635 in f28e74b

$provider->acquireLock('files/' . md5($this->getId() . '::' . trim($path, '/')), $type, $this->getId() . '::' . $path);

Before:

"Documents/test.doc" is locked, existing lock on file: 2 shared lock

After:

"Documents/test.doc" is locked, existing lock on file: 2 shared lock: files/196106b5350a532ce3d8870cac8d466e

[juliushaertl]

Sorry for the noise, I actually missed it is part of the previous exception message