fix: allow updating the virtual cluster using the platform driver

[lizardruss]

What issue type does this pull request address? (keep at least one, remove the others)
/kind bugfix

What does this pull request do? Which issues does it resolve? (use resolves #<issue_number> if possible)
part of ENG-3891

What else do we need to know?
While authoring docs, I found it was not possible to edit a previously created virtual cluster using the CLI command like:

vcluster create my-vcluster --values tests/vcluster.yaml --project default --use

This was due to several issues that are addressed by this PR:

• the platform driver incorrectly detected that the virtual cluster was deployed by helm
• the platform driver was applying option values if any option had changed, resulting in several getting overwritten

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