Allow infinite lock through configuration

[juliushaertl]

Implements https://github.com/nextcloud/files_lock/issues/49

• Allow setting lock_timeout to 0 for not-expiring locks
• Print out expiry details in the occ status command
• Make no expiry the default

[juliushaertl]

Lock TTL would actually make sense to be adjustable depending on their use case.

• WebDAV for example assumes that the lock initiator can specify the TTL
• Collabora could actually use an infinite one, because WOPI will unlock files after they are out of use
• For manual locks a default TTL would still make sense to avoid additional admin load on stale locks