Create a 410 page template

[kathrynwp]

As we prepare to unpublish some of the deprecated tutorials that don't have a newer equivalent, we'll be using a 410 redirect to tell search engines that these pages have been permanently deleted.

We can use the "401 not found" template as a base for the new 410 template, with the addition of a line to request feedback about what the user came looking for.

This can link to https://learn.wordpress.org/report-content-feedback/

Preliminary wording suggestion, but would love @thetinyl and @bsanevans's thoughts:

If you were looking for something specific, please let us know.

Related issues: #2499 #2496 #2393