[CI] Render spec pages without preprocessing

[chalin]

As part of streamlining the tooling used to prepare and render spec pages, I propose that we avoid spec page preprocessing. I originally opted for preprocessing because I didn't think that Hugo could support GitHub docs directly, but it does already (with considerable extra mounts config -- see Can I use README.md instead of _index.md?), and there's a planned feature that will make this much easier and more concise to configure: gohugoio/hugo#10129. We can still make progress in the meantime.

I've decided to start with semconv

Tasks

Semconv

• Tracker issue for front-matter prep: [editorial] Inline Hugo front matter semantic-conventions#1821
• [CI] Script updates in support of semconv spec processing and testing #6084
• [CI] More title normalization tweaks #6089
• [CI] Semconv: mount README.md as _index pages #6103
• ...

OTel spec

TBC