Add jsonencode for clustervariables and nodepool overrides in the tazukubernetescluster resource acceptance tests

[ramya-bangera]

1. What this PR does / why we need it:
   Test fix to include jsonencode for clusterclass variables

2. Which issue(s) this PR fixes

    (optional, in `fixes #<issue number>` format, will close the issue(s) when PR gets merged):
   
    Fixes #
   

3. Additional information
   Test log:

<testsuite name="github.com/vmware/terraform-provider-tanzu-mission-control/internal/resources/testing" tests="0" failures="0" errors="0" id="215" hostname="sc2-10-43-229-72.nimbus.eng.vmware.com" time="0.000" timestamp="2023-12-11T17:14:52Z"></testsuite>
	<testsuite name="github.com/vmware/terraform-provider-tanzu-mission-control/internal/resources/tanzukubernetescluster/tests" tests="1" failures="0" errors="0" id="216" hostname="sc2-10-43-229-72.nimbus.eng.vmware.com" time="1806.351" timestamp="2023-12-11T17:44:53Z">
		<testcase name="TestAcceptanceUTKGResource" classname="github.com/vmware/terraform-provider-tanzu-mission-control/internal/resources/tanzukubernetescluster/tests" time="1806.320">
			<system-out><![CDATA[    tanzu_kubernetes_cluster_test.go:106: Tanzu kubernetes cluster resource acceptance test complete!]]></system-out>
		</testcase>
		<system-out><![CDATA[	github.com/vmware/terraform-provider-tanzu-mission-control/internal/resources/tanzukubernetescluster/tests	coverage: 89.7% of statements]]></system-out>
	</testsuite>

4. Special notes for your reviewer

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (4ac75a1) 25.28% compared to head (48a7925) 25.28%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #351   +/-   ##
=======================================
  Coverage   25.28%   25.28%           
=======================================
  Files         189      189           
  Lines       16345    16345           
=======================================
  Hits         4133     4133           
  Misses      11998    11998           
  Partials      214      214           

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[github-actions]

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