Extending jmespath expressions

[sbera87]

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• Did a review by yourself.
• Added proper tests to cover this PR. (If tests are not applicable, explain.)
• Checked if this PR is a breaking (APIs have been changed) change.
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[sbera87]

 "operationContextParams":{
        "ResourceArnList":{"path":"TransactItems[*].[ConditionCheck.TableName, Put.TableName, Delete.TableName, Update.TableName][]"}

will generate the following code:

//Accessor for dynamic context endpoint params
Aws::Vector<Aws::String> TransactWriteItemsRequest::GetOperationContextParams() const{
  Aws::Vector<Aws::String> result;
  auto& TransactItemsElem = (*this).GetTransactItems();
  for (auto& TransactItemsElem : TransactItemsElem)
  {
  	auto& ConditionCheckElem = TransactItemsElem.GetConditionCheck().GetTableName();
  	result.emplace_back(ConditionCheckElem);
  	auto& PutElem = TransactItemsElem.GetPut().GetTableName();
  	result.emplace_back(PutElem);
  	auto& DeleteElem = TransactItemsElem.GetDelete().GetTableName();
  	result.emplace_back(DeleteElem);
  	auto& UpdateElem = TransactItemsElem.GetUpdate().GetTableName();
  	result.emplace_back(UpdateElem);
  }
  return result;
}

[sbiscigl]

would rather have this handled in the loop than a break statement

while (!this.getVarName().isEmpty() && !this.getVarName().peek().right) {
  this.getVarName().pop();
}

[sbera87]

shall change