[Refactor] Refactor CCE clusters v3

[muneeb-jan]

What this PR does / why we need it

CCE code is using legacy architecture. Most functions such as golangsdk.BuildRequestBody() are depreciated. In this PR, I wish to bring the code up to date with current design and development practices. I also wish to make the code more readable by explicitly specifying the inputs and outputs. Finally, in this PR, the code shall be conformed to API documentation with regards to input and output structs i.e. the function return would be conformed to API response body without the need for extra extract step on part of user.

Which issue this PR fixes

Tests performed

=== RUN   TestListCluster
--- PASS: TestListCluster (0.55s)
=== RUN   TestCluster
--- PASS: TestCluster (405.40s)
=== RUN   TestKubeConfig
--- PASS: TestKubeConfig (434.17s)
PASS