feat: 2.17 release changelog

[mikehardy]

Went through this on google docs already a ton with David

worked on it locally in asciidoc format afterwards with edit/render cycles until it appeared to look good

Posting up here with a soft-approve from David already, checking rendering and re-re-reviewing it

will merge ASAP to get the release kicked off

[mikehardy]

Done with obvious formatting errors, all links checked and they load desired target correctly (one was subtle!) Going to take a break then re-re-re-read it again, the if it looks good merge and start 2.17 release

[mikehardy]

post-break re-read, found some tiny tiny things, I can no longer see anything. Render check is 💯 locally. Good (enough) to go.

We can always do follow-ons after