Support nested variable resolution

[shivdudhani]

Able to process variables like {{configmap.devtest.customData.data.{{serviceAccountName}}}}}

• resolve the value of variable {{serviceAccountName}} -> <value>
• resolve the value of variable{{{configmap.devtest.customData.data.<value>}}

Limitations:

• If the inner variable returns a non-scalar then it is considered as a failed variable, as the outer variable cannot use non-scalar value for evaluation.
• Only equal operation is supported on variables. Handling operators on internal variables is not supported.