This function accepts the strategy and substrategy columns of the data set and create a list of groups as required by the selectizeInput optgroup functionality
create_strategy_optGroups(strategy, substrategy)
a list of groups for strategy/ substrategy as required by the selectizeInput optgroup functionality
strategy column
substrategy column
We assume that substrategies pertaining to a given strategy uses the name of the strategy followed by a period and then the substrategy number. For example, substrategy 2 for strategy 1 must be named "Strategy 1.2".