[release-0.25] Display correct error message when passing Cluster based resource without ClusterClass as part of cluster create

[anujc25]

What this PR does / why we need it

• Display correct error message when passing Cluster based resource without ClusterClass as part of cluster create

Currently, when user passes Cluster resource as part of tanzu cluster create --file <input.yaml> and the cluster resource doesn't include ClusterClass as part of .spec.topology.cluster thrown proper error message.

Which issue(s) this PR fixes

Fixes #3054

Describe testing done for PR

• Added unit tests
• Manually verified by passing --dry-run output to tanzu cluster create --file <manifest.yaml> and verified the error message

Release note

Display correct error message when passing Cluster resource without ClusterClass as part of cluster create

Additional information

Special notes for your reviewer

[github-actions]

Cluster Generation A/B Results:
https://storage.googleapis.com/tkg-clustergen/3076/20220804160633/clustergen.diff.txt
Author/reviewers:
Please review to verify that the effects on the generated cluster configurations are exactly what the PR intended, and give a thumbs-up if so.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (release-0.25@42f1939). Click here to learn what that means.
The diff coverage is n/a.

❗ Current head 5ff2310 differs from pull request most recent head f1f9cf9. Consider uploading reports for the commit f1f9cf9 to get more accurate results

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[github-actions]

Cluster Generation A/B Results:
https://storage.googleapis.com/tkg-clustergen/3076/20220805164206/clustergen.diff.txt
Author/reviewers:
Please review to verify that the effects on the generated cluster configurations are exactly what the PR intended, and give a thumbs-up if so.

[github-actions]

Cluster Generation A/B Results:
https://storage.googleapis.com/tkg-clustergen/3076/20220805171105/clustergen.diff.txt
Author/reviewers:
Please review to verify that the effects on the generated cluster configurations are exactly what the PR intended, and give a thumbs-up if so.

[github-actions]

Cluster Generation A/B Results:
https://storage.googleapis.com/tkg-clustergen/3076/20220805175848/clustergen.diff.txt
Author/reviewers:
Please review to verify that the effects on the generated cluster configurations are exactly what the PR intended, and give a thumbs-up if so.

[chandrareddyp]

LGTM!

[github-actions]

Cluster Generation A/B Results:
https://storage.googleapis.com/tkg-clustergen/3076/20220805202051/clustergen.diff.txt
Author/reviewers:
Please review to verify that the effects on the generated cluster configurations are exactly what the PR intended, and give a thumbs-up if so.

[github-actions]

Cluster Generation A/B Results:
https://storage.googleapis.com/tkg-clustergen/3076/20220805224817/clustergen.diff.txt
Author/reviewers:
Please review to verify that the effects on the generated cluster configurations are exactly what the PR intended, and give a thumbs-up if so.