Bootstrap copied BFF and local accounts with public Sendico contracts (#34)

backend/contracts/sendico/external/chain_network.yaml

@@ -0,0 +1,10 @@
+components:
+  schemas:
+    ChainNetwork:
+      type: string
+      enum:
+        - unspecified
+        - ethereum_mainnet
+        - arbitrum_one
+        - tron_mainnet
+        - tron_nile