add Connection.use_(certificate|privatekey)

[mhils]

(depends on cryptography 38)

Follow-up to pyca/cryptography#7210. :)
I've added comments to point out the duplication between Context and Connection. Let me know if you want those out, happy to adjust to whatever style you prefer.

[reaperhulk]

cryptography 38 is out now 😄

[reaperhulk]

Conflict here due to the new pinning, but we should get this reviewed ASAP 😄

[mhils]

Conflict fixed! 😃

[balloob]

This PR has not updated the changelog. Changelog for 22.1 still mentions Cryptography 37 as the minimum version.

[reaperhulk]

@balloob Thanks for the report, we've got a changelog fix up in #1150 although we may also need to spin some knobs on readthedocs as well since this won't fix the stable tag.