feat(socket source, syslog source): allow custom permissions on socket (#12115)

* feat(socket/syslog source): allow custom permissions on socket

This patch adds a new option : `socket_file_mode` to the socket and
syslog sources to set the permission on the created unix socket.

Fixes #9241

Signed-off-by: Patrik Cyvoct <patrik@ptrk.io>

* expand guard on unix

Signed-off-by: Patrik Cyvoct <patrik@ptrk.io>

* final fix ?

Signed-off-by: Patrik Cyvoct <patrik@ptrk.io>

* should be good

Signed-off-by: Patrik Cyvoct <patrik@ptrk.io>

* fix review

Signed-off-by: Patrik Cyvoct <patrik@ptrk.io>

* fix review bis

Signed-off-by: Patrik Cyvoct <patrik@ptrk.io>