Change log for POSTFIX_MAIL

Date Changes
2024-06-25 Enhancement:
- Added support to parse new format of syslog logs.
2024-05-22 Enhancement
- Added a Grok pattern to extract "from" and "to" email addresses, "subject", and "filename" from the raw log and set "metadata.event_type" to "EMAIL_TRANSACTION".
2022-10-06 Enhancement
- Modified grok pattern to parse the logs.
2022-07-18 Enhancement
- Mapped host.hostname to principal.hostname.
- Mapped host.ip to principal.ip.
- Mapped host.mac to principal.mac.
- Mapped host.id to principal.asset.asset_id.
- Mapped host.os.name to principal.platform.
- Mapped network.ip_protocol to TCP if input.type is tcp.
- Mapped log.source.address data src_ip to principal.ip, src_port to principal.port.
- Mapped agent.id to metadata.product_log_id.
- Mapped agent.type to metadata.product_event_type.
- Mapped agent.version to metadata.product_version.
- Mapped source_ip to principal.ip.
- Mapped source_hostname to principal.hostname.
- Mapped target_email to network.email.to if it is an email else mapped to target.user.userid.
- Mapped from_user to network.email.from.