Add random choice support for WeightedSwitchController

[KopysovDB]

WeightedSwitchController.md

Random Choice - on each iteration plugin will choose a random item. This check box can not guarantee that actual percent of child elements execution will equals with expected (delta in tests not more than 0.5%)

• Added isRandomChoice() method to DslWeightedSwitchController to enable random selection of child elements
• Added test case to verify random choice functionality

weightedSwitchController() .child(weight1, httpSampler(SAMPLE_1_LABEL, wiremockUri)) .children(httpSampler(SAMPLE_2_LABEL, wiremockUri)) .child(weight2, httpSampler(label3, wiremockUri)) .isRandomChoice()