net/rabbitmq: Update 4.2.0 => 4.2.2

Changelogs:
https://github.com/rabbitmq/rabbitmq-server/releases/tag/v4.2.1
https://github.com/rabbitmq/rabbitmq-server/releases/tag/v4.2.2

Improve port:

• Parametrize "rabbitmq" with "${PORTNAME}".
• Use "WRKSRC=*" instead of custom "do-extract".
• Remove unnecessary ".include <bsd.port.options.mk>".
• Use ETCDIR.
• Merge MKDIRs and COPYTREE_BINs.
• Replace "LN -s" with "RLN".

MFH: 2026Q1