man/doveconf: Add -U parameter

Author: sirainen

.github/actions/spelling/patterns.txt

@@ -106,7 +106,8 @@ BBAAAAAAAAAAAAAAAAAAAAAAB
 d88ff1001d4bf753a1b800001accfe22
 &U,BTFw-
 &ZeVnLIqe-
--adnPNx
+-adn
+PNUx
 F=DFMPhnu9,
 SPfne
 \bAPPEND(?:ed|s)

docs/core/man/doveconf.1.md

@@ -9,7 +9,7 @@ dovecotComponent: core
 ## SYNOPSIS
 
 **doveconf**
-  [**-adnPNx**]
+  [**-adnPNUx**]
   [**-c** *config-file*]
   [**-f** *filter*]
 
@@ -94,6 +94,9 @@ configuration in easy human readable output.
 **-P**
 :   Show passwords and other sensitive values.
 
+**-U**
+:   Ignore all unknown settings in config file.
+
 **-x**
 :   Expand configuration variables (e.g. `$ENV:foo`) and show file contents
     (from e.g. `ssl_server_key_password = \</etc/ssl/password.txt`).