Preserve connection order in Blinker

[avaris]

Resolves: #2564

One caveat: as written in the docs change, the only way to order auto-discovered namespace plugins is to disable auto-discovery and specify order explicitly with PLUGINS setting.

• Ensured tests pass and (if applicable) updated functional test output
• Conformed to code style guidelines by running appropriate linting tools
• Added tests for changed code
• Updated documentation for changed code

[justinmayer]

Excellent work, @avaris. Bravo! 🎊