Change log for PROOFPOINT_SENDMAIL_SENTRION

Date Changes
2024-06-05 Enhancement:
- Mapped "subject" to "network.email.subject".
2024-05-22 - Added a Grok pattern over "message" to parse a new log type.
- Added a Grok over "kv_data" to extract the field "subject".
- Mapped "subject" to "security_result.detection_fields".
2024-03-07 - Newly created parser.