Add new relaying env. vars. (#160)

Adds new sample env. vars. for [the extension of 'relayable' chains](safe-global/safe-client-gateway#1970):

- Add env. vars. for: Optimism, BSC, Polygon, Polygon zkEVM, Base, Avalanche, Linea and Blast.

container_env_files/cgw.env

@@ -64,8 +64,16 @@ PUSH_NOTIFICATIONS_API_SERVICE_ACCOUNT_PRIVATE_KEY=''
 # (default=5)
 # RELAY_THROTTLE_LIMIT=
 # The API key to be used per chain.
-RELAY_PROVIDER_API_KEY_ARBITRUM_ONE=''
+RELAY_PROVIDER_API_KEY_OPTIMISM=''
+RELAY_PROVIDER_API_KEY_BSC=''
 RELAY_PROVIDER_API_KEY_GNOSIS_CHAIN=''
+RELAY_PROVIDER_API_KEY_POLYGON=''
+RELAY_PROVIDER_API_KEY_POLYGON_ZKEVM=''
+RELAY_PROVIDER_API_KEY_BASE=''
+RELAY_PROVIDER_API_KEY_ARBITRUM_ONE=''
+RELAY_PROVIDER_API_KEY_AVALANCHE=''
+RELAY_PROVIDER_API_KEY_LINEA=''
+RELAY_PROVIDER_API_KEY_BLAST=''
 RELAY_PROVIDER_API_KEY_SEPOLIA=''
 
 # Staking Provider