Clarify subsection ID syntax in assemblies

[adellape]

trafficstars

• Per team discussion, add clarification/exception about not using {context} variables in assembly subheading anchor IDs (Preview)
• Slight reflowing of the "Assembly/module titles and section headings" section for clarity, most notably moving "Discrete headings" as the last subsection:
• Update some older example blocks that were using either manually-bolded titles or an unnecessary lead-in section to just use a .Example style block title

[ocpdocs-previewbot]

🤖 Wed Jun 05 16:23:15 - Prow CI generated the docs preview:

https://71472--ocpdocs-pr.netlify.app/

[openshift-ci[bot]]

New changes are detected. LGTM label has been removed.

[adellape]

Putting this through peer review again because it has had some significant changes since the last round, not least of which flipping on what the actual advice is. 😅

[openshift-ci[bot]]

@adellape: all tests passed!

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