Include allowed presets in err msg

[lkysow]

consul-k8s install -preset demo
'demo' is not a valid preset

=>

consul-k8s install -preset demo                                                                                                                                                                                                                                                                                                                      
'demo' is not a valid preset (valid presets: cloud, quickstart, secure)

How I've tested this PR:

• manually and with tests added

How I expect reviewers to test this PR:

• 👀

Checklist:

• Tests added
• CHANGELOG entry added

  HashiCorp engineers only, community PRs should not add a changelog entry.
  Entries should use present tense (e.g. Add support for...)

[lkysow]

Not sure this one is worth a changelog?

[jmurret]

🎉 Thank you! this is great.