SecuritiesListing - consider whether the two MIC fields might be better structured

[kd-ods]

Summary of the bug or issue
The two MIC fields operatingMarketIdentifierCode and marketIdentifierCode in the SecuritiesListing object have clunky descriptions. Additionally the validation is complicated since whether the exchange is a segment can only be inferred from the two MIC values (rather than being explicitly stated). All of this is somewhat a by-product of ISO 10383 itself. Nevertheless, there may be a nicer way of doing things.

Suggested resolution
One option to consider would be pushing the stock exchange info down a level and adding an isSegment boolean field, so:

"stockExchange": {
   "name": "XXX"
   "jurisdiction": "XX"
   "isSegment": T/F
   "marketIdentifierCode": "XXX"
   "operatingMarketIdentifierCode": "XXX"
}