feat: add support for Dovecot IMAP/POP3 configuration

Introduces functionality to install and configure Dovecot alongside Postfix to provide IMAP/POP3 services.

Changes include:
- Added tasks to install Dovecot packages (core, imapd, pop3d, lmtpd).
- Added templates for main configuration and conf.d files (auth, master, ssl, mail).
- Defined default variables for protocols, SSL settings, and Maildir location.
- Enabled Postfix SASL and LMTP integration options.
- Added a handler to restart the Dovecot service.
- Updated README.md with the new configuration variables and usage instructions.

templates/10-master.conf.j2

@@ -0,0 +1,51 @@
+# Dovecot master configuration
+# Ansible managed: {{ ansible_managed }}
+
+service imap-login {
+  inet_listener imap {
+    port = 143
+  }
+  inet_listener imaps {
+    port = 993
+    ssl = yes
+  }
+}
+
+service pop3-login {
+  inet_listener pop3 {
+    port = 110
+  }
+  inet_listener pop3s {
+    port = 995
+    ssl = yes
+  }
+}
+
+service lmtp {
+  unix_listener /var/spool/postfix/private/dovecot-lmtp {
+    mode = 0600
+    user = postfix
+    group = postfix
+  }
+}
+
+service auth {
+  unix_listener /var/spool/postfix/private/auth {
+    mode = 0660
+    user = postfix
+    group = postfix
+  }
+
+  unix_listener auth-userdb {
+    mode = 0600
+    user = vmail
+  }
+}
+
+service auth-worker {
+}
+
+service dict {
+  unix_listener dict {
+  }
+}