[ECS] Fix unexpected diff of Plan Preview

[t-kikuc]

What this PR does:

• Clone manifests in DriftDetection not to modify the original ones in AppManifestsCache.

NOTE: I'll fix Lambda too, it has the same problem.

Why we need it:

• Without this PR, unexpected diff appears in ECS PlanPreview.

  e.g. Subnets, Essential, and Protocol are unexpected.

  

• The cause is that ignoreAndSortParameters() in ECS DriftDetection unintentionally overwrites ECS manifests in AppManifestsCache.

  • PlanPreview loads manifests from AppManifestsCache. The cache is shared with DriftDetection. https://github.com/pipe-cd/pipecd/blob/3a264ccdf57521bd433f6599203cc6eb51252d09/pkg/app/piped/planpreview/ecsdiff.go#L59
  • It is values of pointer targets in the cache that are overwritten. Cache values themselves are not overwritten.

Which issue(s) this PR fixes:

Does this PR introduce a user-facing change?:

• How are users affected by this change:
• Is this breaking change:
• How to migrate (if breaking change):

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 86.95652% with 3 lines in your changes missing coverage. Please review.

Project coverage is 25.23%. Comparing base (c842a89) to head (48ea969). Report is 8 commits behind head on master.

Files with missing lines	Patch %	Lines
pkg/app/piped/driftdetector/ecs/detector.go	86.95%	3 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #5306 +/- ## ========================================== + Coverage 25.02% 25.23% +0.20% ========================================== Files 447 444 -3 Lines 47520 47480 -40 ========================================== + Hits 11892 11980 +88 + Misses 34690 34559 -131 - Partials 938 941 +3 ```

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