in_forward: support 'unix_perm' (#815)

Signed-off-by: Takahiro Yamashita <[email protected]>

Author: nokute78

pipeline/inputs/forward.md

@@ -12,6 +12,7 @@ The plugin supports the following configuration parameters:
 | Listen              | Listener network interface.                                                                                                                                                                                                                                                                                                                 | 0.0.0.0 |
 | Port                | TCP port to listen for incoming connections.                                                                                                                                                                                                                                                                                                | 24224 |
 | Unix_Path           | Specify the path to unix socket to receive a Forward message. If set, `Listen` and `Port` are ignored.                                                                                                                                                                                                                                      | |
+| Unix_Perm           | Set the permission of the unix socket file. If `Unix_Path` is not set, this parameter is ignored.                                                                                                                                                                                                                                      | |
 | Buffer\_Max\_Size   | Specify the maximum buffer memory size used to receive a Forward message. The value must be according to the [Unit Size](../../administration/configuring-fluent-bit/unit-sizes.md) specification.                                                                                                                                          | 6144000 |
 | Buffer\_Chunk\_Size | By default the buffer to store the incoming Forward messages, do not allocate the maximum memory allowed, instead it allocate memory when is required. The rounds of allocations are set by _Buffer\_Chunk\_Size_. The value must be according to the [Unit Size ](../../administration/configuring-fluent-bit/unit-sizes.md)specification. | 1024000 |
 | Tag_Prefix          | Prefix incoming tag with the defined value.|  |