textproc/kibana8: Port improvements that were made while creating ports of version 9.x

• Improved text in COMMENT, pkg-deinstall, pkg-message, pkg-descr.
• Parametrize kibana with ${PORTNAME} in CONFLICTS.
• Add possibility to run port with non-default user/group www.
• Fix indents in post-patch.
• Refresh patches.

PR: 290979
Approved by: elastic (maintainer, implicit - inactive for more than 6 months)