doveadm: Fill out example information for commands

Also add missing text descriptions.

Author: slusarz

.github/actions/spelling/expect.txt

@@ -562,6 +562,7 @@ offenburg
 OIDC
 olc
 oldkey
+oldpassword
 oldpath
 oldstats
 onelevel
@@ -800,6 +801,7 @@ testmbox
 testpass
 testshared
 textcat
+textprefix
 thead
 tika
 tikahost