State of Unit going forward

[ac000]

This is a repost of https://unit.nginx.org/community/#maintenance-and-support-guidelines

Going forward, NGINX Unit will no longer receive new features or enhancements from the project maintainers. NGINX Unit is still open to community contributions.

The team is focusing its limited capacity to keep NGINX Unit stable, secure and high-quality. Its focus will be on critical maintenance, such as for security issues, dependency upgrades, and resolving crashes or undefined behavior.