Merge #14688: Doc: update release notes for changes since 0.17.0 branch

<pre>Merge #14688: Doc: update release notes for changes since 0.17.0 branch ba8f0c6c8d6d3f5b0bd0ab92b6a4ca9f7b5f0862 Release notes: integrate detached release notes (David A. Harding) 6062f0e6139cfc5802e9b18f03908191d8c530f5 Release notes: update notes through to 11e1ac3ae08 (David A. Harding) Pull request description: This documents changes listed by `git log v0.17.0...11e1ac3 --merges` and integrates the existing detached release notes into the main file. My goal is to update the release notes each month in order to reduce the amount of writing and review that needs to be done all at once near the start of the RC cycle. Note: I've chosen to use fully-qualified URLs for linking to documentation, rather than shorter relative URLs that would otherwise be preferred, as the release notes are commonly copied into emails, reddit threads, and blog posts where relative URLs would be incomplete or would point to the wrong page. Tree-SHA512: a943327d48e166f4a188ab0f468972609276e9c8f0ed85513823511ed989606445bf6b0ae9dd693b5d1e13d2f98c13573acd13865c57fe9c8ee9dbd04ceeff7f</pre>