Doc pages table of contents are inconsistent

[mindrones]

Some pages have a complete table of content where each link correspond to a section title anchor, like [1], some others seem to have an incomplete TOC, like [2], while some don't have the TOC at all, like [3].

Having a consistent TOC would be really great!

[1] https://www.elastic.co/guide/en/elasticsearch/reference/7.10/search-aggregations-bucket-autodatehistogram-aggregation.html#_intervals
[2] https://www.elastic.co/guide/en/elasticsearch/reference/7.10/search-aggregations-bucket-datehistogram-aggregation.html#calendar_intervals
[3] https://www.elastic.co/guide/en/elasticsearch/reference/7.10/search-aggregations-metrics-geobounds-aggregation.html

[elasticmachine]

Pinging @elastic/es-docs (Team:Docs)

[lockewritesdocs]

Thanks for bringing this issue to our attention @mindrones! I opened PR #66604 to fix some of the heading issues and provide a more consistent TOC. We're working on many improvements to our documentation system that will address these kinds of issues.