[stable34] fix(wopi): report a locked file as 423, not 500 - #6063

When putContent() throws LockedException the file is locked by another
operation and we have written nothing. Answering 500 says the server is
broken, which it isn't, and it buries a routine, self-resolving
condition in the error logs.

It also misleads the editor. Collabora Online cannot tell a genuine
fault from a refusal, so after the failed upload it asks for
CheckFileInfo to work out whether the document in storage is still the
one it knows. A 423 lets it see the upload for what it was and retry
once the lock clears.

423 is what this controller already answers with when the lock manager
reports a file locked in lock() and refreshLock(); use it on the write
path too.

Do not use 409: in WOPI that means the document changed in storage, and
Collabora Online reads it that way. It would put a conflict dialog in
front of the user, asking them to discard their work or overwrite a file
that nobody has touched.

Signed-off-by: Andras Timar <andras.timar@collabora.com>