R1:c21a71f02489

Cache generation of the SSH authentication keyfile for sshd

Summary:
Ref T11469. This isn't directly related, but has been on my radar for a while: building SSH keyfiles (particular for installs with a lot of keys, like ours) can be fairly slow.

At least one cluster instance is making multiple clone requests per second. While that should probably be rate limited separately, caching this should mitigate the impact of these requests.

This is pretty straightforward to cache since it's exactly the same…