wk1: initial docker image setup

target/dovecot/90-plugin.conf

@@ -0,0 +1,11 @@
+##
+## Plugin settings
+##
+
+# All wanted plugins must be listed in mail_plugins setting before any of the
+# settings take effect. See <doc/wiki/Plugins.txt> for list of plugins and
+# their configuration. Note that %variable expansion is done for all values.
+
+plugin {
+  #setting_name = value
+}