[Meta] Tighten-up Output Workers for 5.0 Release

[andrewvc]

A lot has changed in preparation for 5.0 we need to tighten up a lot of our output worker story before 5.0 . This meta issue will track those changes. Ultimately, we'd love to get rid of output workers(#5653) but that will probably have to wait till 6.0.

• Educate: Performance Tuning Guide
• Educate: Blog detailing changes and internals of pipeline architecture.
• Improve nomenclature and methods for 'threadsafe' outputs
• Remove instance method version of workers_not_supported
• Raise Error when output_workers set for threadsafe plugin
• Enforce unique ID for plugins
• Modify docs generator to correctly tag threadsafe outputs
• Implement Codec#multi_encode / Output#multi_receive_encoded
• Mass update plugins to conform to new output delegator
• Output plugins not receiving metrics
• Add workers_not_supported obsolescence message
• Improve OD public API

[suyograo]

Added blog and docs item as well.