Update packer example template

[sdarwin]

When running packer to generate an image, the user will likely consider changing the template from ubuntu-2104 to ubuntu-2204, since that's a long term support version and it's newer. After making that change, packer will fail. The reason is not obvious. After logging into the build machine it says userauth_pubkey: key type ssh-rsa not in PubkeyAcceptedAlgorithms The solution is to add temporary_key_pair_type.

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[ejv]

As of Packer release version 1.8.1, it is no longer necessary to declare temporary_key_pair_type in the build configuration (users will want to ensure they are using a contemporary version of Packer).

I've included the change to the source_image_family in #604 (updating to Packer release version 1.8.5).

I recommend closing this PR. Thanks for your contribution.