dovecot: add Flatcurve FTS Engine as EXPERIMENTAL (#5920)

* dovecot: experimental added flatcurve backend + switch

* dovecot: bump docker image

data/conf/dovecot/dovecot.conf

@@ -10,6 +10,7 @@
 auth_mechanisms = plain login
 #mail_debug = yes
 #auth_debug = yes
+#log_debug = category=fts-flatcurve # Activate Logging for Flatcurve FTS Searchings
 log_path = syslog
 disable_plaintext_auth = yes
 # Uncomment on NFS share
@@ -194,9 +195,6 @@ plugin {
   acl_shared_dict = file:/var/vmail/shared-mailboxes.db
   acl = vfile
   acl_user = %u
-  fts = solr
-  fts_autoindex = yes
-  fts_solr = url=http://solr:8983/solr/dovecot-fts/
   quota = dict:Userquota::proxy::sqlquota
   quota_rule2 = Trash:storage=+100%%
   sieve = /var/vmail/sieve/%u.sieve
@@ -305,6 +303,7 @@ replication_dsync_parameters = -d -l 30 -U -n INBOX
 !include_try /etc/dovecot/extra.conf
 !include_try /etc/dovecot/sogo-sso.conf
 !include_try /etc/dovecot/shared_namespace.conf
+!include_try /etc/dovecot/conf.d/fts.conf
 # </Includes>
 default_client_limit = 10400
 default_vsz_limit = 1024 M