Simplify multiplexed transport API (micro-frontends/module metadata)

[maxkosty]

Problem Statement

Filing this to track.
Current solution has room to be simplified and still cover majority use cases.
We want to avoid customers being turned off by complexity and seeking non-supported solutions on their own. Our recent experience with a 3-4 sales-led customers suggests current doc+solution is not straightforward enough.

Related: getsentry/sentry-docs#9215

Solution Brainstorm

See comments in #10798

[AbhiPrasad]

We've evaluated this a bunch these past couple months but I don't think it's a high priority item compared to everything else.

For now going to close as a won't do - but we will definitely re-evaluate this in the future.