Use upstream's MergeValues with assets

[blampe]

Followup to my comment here, this removes our custom ValueOpts in favor of upstream's value.Options to handle merging.

Upstream expects to work with files on disk, so we fetch any assets in our provided values and then write them to disk temporarily.

[github-actions[bot]]

Does the PR have any schema changes?

Looking good! No breaking changes found. No new resources/functions.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 65.85366% with 14 lines in your changes are missing coverage. Please review.

Project coverage is 32.29%. Comparing base (675c630) to head (cadae3a). Report is 1 commits behind head on master.

Files	Patch %	Lines
provider/pkg/provider/helm/v4/values.go	63.63%	7 Missing and 5 partials :warning:
provider/pkg/provider/helm/v4/chart.go	75.00%	1 Missing and 1 partial :warning:

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3010   +/-   ##
=======================================
  Coverage   32.29%   32.29%           
=======================================
  Files          69       69           
  Lines        8947     8963   +16     
=======================================
+ Hits         2889     2895    +6     
- Misses       5791     5796    +5     
- Partials      267      272    +5     

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[EronWright]

On one hand, this approach allows us to leverage more of the Helm library, specifically related to loading values files. On the other hand, the need to write out the adhoc values to a file seems a bit contrived. Let's vote on it, in description.