Integrate the OTel specification into the website

[chalin]

• Publish the specification via opentelemetry.io #852
• Ensure that links to the spec are local #908
• Update spec submodule to v1.8.0 #921
• Update opentelemetry-specification to v1.9.0 #1131
• Fix spec 404s:
  • Specification > Project Package Layout: some TOC entries result in 404s #935
    • [editorial] Library layout: fix headings to avoid 404s opentelemetry-specification#2136
  • Remove the following ignore rules:

    opentelemetry.io/.htmltest.yml

    Lines 5 to 10 in 2ae73ac

    	# TODO: fix the source of these inlined TOC links
    	- HAHAHUGOSHORTCODE-s0-HBHB
    	- HAHAHUGOSHORTCODE-s1-HBHB
    	- HAHAHUGOSHORTCODE-s2-HBHB
    	- HAHAHUGOSHORTCODE-s5-HBHB
    	- HAHAHUGOSHORTCODE-s7-HBHB

    
    Done via:
  • Update opentelemetry-specification to v1.9.0 #1131
  • Link check: remove ignore rules now that spec has been fixed #1135
• Sections with missing index pages:
  • Propose moving project/repo-level ToC into a new specification/README.md -- [editorial] Move spec TOC into the spec opentelemetry-specification#2444
  • Prep work:
    • [editorial] Ensure all ToCs are generated using markdown-toc opentelemetry-specification#2146
    • Config cleanup: drop contentDir, and params with default values #1151
    • Specification: rework of how the spec is generated, and link fix #1152
  • Progress on [editorial] Ensure every section has a README opentelemetry-specification#2558

Other:

• Move redirect rules into front matter of spec pages #1372
• Consider publishing Compliance of Implementations with Specification under /reference/specification or just under /reference.
• Consider using the render-link hook instead of preprocessing links in the markdown. Related:
  • https://discourse.gohugo.io/t/how-to-make-relative-hyperlinks-work-the-github-way/35601
  • https://github.com/bep/portable-hugo-links/blob/master/layouts/_default/_markup/render-link.html

[chalin]

I'm exploring bringing in the (adjusted) spec pages via a mount, but have run into a snag. For details, see https://discourse.gohugo.io/t/content-mount-problem-for-single-language-multilingual-site/37215.

[chalin]

I'm going to consider this done:

• The spec has been successfully integrated (via a git submodule) using an adjust-mardown script.
• Interestingly, the spec pages account for 13-15% of the non-homepage website traffic!

We can continue to track the remaining issue separately via the following, since it is a "longer-term" improvement task that is addressed incrementally with each spec release (~ monthly):

• [editorial] Ensure every section has a README opentelemetry-specification#2558