Add security prices provider (Synth integration) (#1039)

* User tickers as primary lookup symbol instead of isin

* Add security price provider

* Fetch security prices in bulk to improve sync performance

* Fetch prices in bulk, better mocking for tests

.env.test.example

@@ -0,0 +1,17 @@
+# ================
+# Data Providers
+# ---------------------------------------------------------------------------------
+# Uncomment and fill in live keys when you need to generate a VCR cassette fixture
+# ================
+
+# SYNTH_API_KEY=<add live key here>
+
+# ================
+# Miscellaneous
+# ================
+
+# Set to true if you want SimpleCov reports generated
+COVERAGE=false
+
+# Set to true to run test suite serially
+DISABLE_PARALLELIZATION=false