Finnhub: use OANDA instead of FHFX for forex symbols (#3955)

* market-status: use finnhub instead of finnhub-secondary

* use finnhub-secondary includes and overrides with finnhub

* add changesets

* fix tests

* revert market-status changes

* update changeset

* remove XPT override

* update changeset

Author: calvwang9

.changeset/dirty-tomatoes-dream.md

@@ -0,0 +1,5 @@
+---
+'@chainlink/finnhub-adapter': major
+---
+
+Use `overrides.json` and `includes.json` from finnhub-secondary. The finnhub adapter will no longer use FHFX forex symbols, and instead use OANDA - this is technically a breaking change, but upgrading to this version will not break any existing feeds.