mail/postsrsd: Update to 2.0.8

This release is a new generation of postsrsd. This update includes:

• support for redis
• support for sqlite3
• disable installing postsrsd.secret - it is generated during first start of postsrsd (startup script)
• add pkg-message which informs about changes in configuration
• some cleanup suggested by portlint

Changelog: https://github.com/roehling/postsrsd/releases/tag/2.0.8

PR: 273571