fix(controller): Move v4 client instantiation to reconcileDelete

[thunderboltsid]

In order to reduce the number of calls made to /prism_central to establish whether a v4 client can be created, we move the v4 client creation to reconcileDelete function as currently that's the only place where we need to make v4 VG detach calls. This ensures we don't impact the regular reconcile cycle and all the new calls only take place on the delete path.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 7.81250% with 59 lines in your changes missing coverage. Please review.

Project coverage is 31.14%. Comparing base (fb76b4f) to head (68e55a6).

Files	Patch %	Lines
controllers/nutanixmachine_controller.go	7.81%	59 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #465 +/- ## ========================================== + Coverage 29.33% 31.14% +1.80% ========================================== Files 14 14 Lines 1476 1477 +1 ========================================== + Hits 433 460 +27 + Misses 1043 1017 -26 ```

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