Re-architect BigPipe to use hx-streaming

Problem/Motivation

The BigPipe implementation has been refactored sufficiently to remove the dependence on jQuery but does not naturally implement an HTML delivery structure for all content.

Proposed resolution

Explore building up a new BigPipe implementation based on the hx-streaming extension for HTMX.

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet