[Merge] ~jchittum/livecd-rootfs:jammy-vagrant-more-secure-private-key into livecd-rootfs:ubuntu/master

[John Chittum]

John Chittum has proposed merging ~jchittum/livecd-rootfs:jammy-vagrant-more-secure-private-key into livecd-rootfs:ubuntu/master.

Commit message:
fix: move Vagrant 22.04+ to ephemeral ed25519 key
    
LP: 1969664 tracks an issue related to the deprecation of rsa+ssh on
Jammy+ openssh server, coupled with upstream vagrant bugs, that cause
Jammy vagrant images fail to bootstrap due to ssh negotiation issues.
Moving to a different key algo from the upstream insecure key matches
Jammy's expectations, and works with older vagrant versions.
  
vagrant >= 2.2.16 hosts are unaffected by the issue, as an upstream
change was made. This change keep compatibility with newer vagrant
versions as well.


Requested reviews:
  Ubuntu Core Development Team (ubuntu-core-dev)

For more details, see:
https://code.launchpad.net/~jchittum/livecd-rootfs/+git/livecd-rootfs/+merge/420024

Testing:

created an image with ubuntu-bartender for testing
uploaded to https://people.canonical.com/~jchittum/vagrant-testing/
tested in a focal VM with the following:

```
apt-get update && apt-get dist-upgrade
apt-get install virtualbox vagrant
vagrant box add ubuntu-jammy-vagrant-TESTING-20220419.box --name jammy-testing-20220419
vagrant init jammy-testing-20220419
vagrant up
```

vagrant succeeded in bootstrapping, with SSH able to reconnect with the provided insecure key. Previous behaviour was SSH timing out as retries failed due to negotiation failure
-- 
Your team Ubuntu Core Development Team is requested to review the proposed merge of ~jchittum/livecd-rootfs:jammy-vagrant-more-secure-private-key into livecd-rootfs:ubuntu/master.
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