* VAULT-29583: Modernize default distributions in enos scenarios
Our scenarios have been running the last gen of distributions in CI.
This updates our default distributions as follows:
- Amazon: 2023
- Leap: 15.6
- RHEL: 8.10, 9.4
- SLES: 15.6
- Ubuntu: 20.04, 24.04
With these changes we also unlock a few new variants combinations:
- `distro:amzn seal:pkcs11`
- `arch:arm64 distro:leap`
We also normalize our distro key for Amazon Linux to `amzn`, which
matches the uname output on both versions that we've supported.
Signed-off-by: Ryan Cragun <me@ryan.ec>