feat(openem): hackily add exchanges (#8289)

* qol refactor

* wip

* wip

* feat(openem): add australian exchanges

* cleanup

* more cleanup

* fix filter

* fix

* typo

* remove autouse=True

* rename existing response json

* au-nsw->au-qld exchange snapshot

* use Exchange in return type

* add au-nsw->au-vic exchange snapshot

* correctly implement exchange events list

* type annotation was too specific

* remove import

Author: seljaks