Refresh evergreen WNP for developer edition

[slightlyoffbeat]

Current Link: https://www.mozilla.org/en-US/firefox/100.0a2/whatsnew/

[alexgibson]

Throwing in some ideas that may help to keep an evergreen page engaging without needing regular updates:

• Show a Dev Tools feature highlight (maybe we could cycle through different features from a finite list, so each release shows something different).
• Feature a random MDN article / link each update.
• Pull in hacks blog post feed.
• Link to dev edition release notes!

[alexgibson]

We should also try and cover the /firstrun page here (right now both /firstrun and /whatsnew share the same template)

[slightlyoffbeat]

Another idea: include a unit to let users know about MDN+

[stephaniehobson]

Another idea: link to the release notes.

[stephaniehobson]

Another idea: Open the release notes.

[alexgibson]

@slightlyoffbeat could we just retire this page and redirect to the release notes page, if this is something we're no longer planning to do?

[stephaniehobson]

Superseded by #14244