add ytt overlay customization warning message

[996refuse]

No description provided.

[github-actions]

Cluster Generation A/B Results:
https://storage.googleapis.com/tkg-clustergen/3819/20221102075123/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/3819/20221102085605/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

Merging #3819 (4dfd970) into main (485f0ce) will decrease coverage by 0.93%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##             main    #3819      +/-   ##
==========================================
- Coverage   46.58%   45.64%   -0.94%     
==========================================
  Files         400      425      +25     
  Lines       39722    41350    +1628     
==========================================
+ Hits        18504    18876     +372     
- Misses      19519    20760    +1241     
- Partials     1699     1714      +15     

Impacted Files	Coverage Δ
tkg/client/cluster.go	15.48% <0.00%> (-0.18%)	⬇️
tkg/client/upgrade_cluster.go	44.57% <0.00%> (-0.05%)	⬇️
tkg/clusterclient/clusterclient.go	48.49% <0.00%> (-0.85%)	⬇️
tkg/client/init.go	0.00% <0.00%> (ø)
tkg/client/delete_region.go	0.00% <0.00%> (ø)
cmd/cli/plugin/cluster/get_node_pools.go	10.52% <0.00%> (ø)
...in/cluster/get_machinehealthcheck_control_plane.go	11.11% <0.00%> (ø)
.../cli/plugin/cluster/get_machinehealthcheck_node.go	9.30% <0.00%> (ø)
cmd/cli/plugin/cluster/osimage_oracle.go	3.22% <0.00%> (ø)
.../cli/plugin/cluster/set_machinehealthcheck_node.go	23.33% <0.00%> (ø)
... and 24 more

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