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/main.cf.j2

@@ -48,3 +48,21 @@ smtp_tls_security_level = may
 # Other settings
 alias_maps = hash:/etc/aliases
 alias_database = hash:/etc/aliases
+
+# Dovecot Integration
+{% if dovecot_enabled | default(false) %}
+# Use Maildir format
+home_mailbox = Maildir/
+
+{% if dovecot_postfix_sasl_enable | default(false) %}
+# SASL Authentication via Dovecot
+smtpd_sasl_type = dovecot
+smtpd_sasl_path = private/auth
+smtpd_sasl_auth_enable = yes
+{% endif %}
+
+{% if dovecot_postfix_lmtp_enable | default(false) %}
+# Delivery via LMTP
+mailbox_transport = lmtp:unix:private/dovecot-lmtp
+{% endif %}
+{% endif %}