allow custom rpc url for katana and madara (#1031)

BUGFIX:
Cannot choose the RPC URL for Katana as STARKNET_NETWORK

Breaks Kakarot-Rpc

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scripts/constants.py

@@ -45,15 +45,15 @@
     "katana": {
         "name": "katana",
         "explorer_url": "",
-        "rpc_url": "http://127.0.0.1:5050",
+        "rpc_url": os.getenv("KATANA_RPC_URL", "http://127.0.0.1:5050"),
         "devnet": True,
         "check_interval": 0.01,
         "max_wait": 1,
     },
     "madara": {
         "name": "madara",
         "explorer_url": "",
-        "rpc_url": "http://127.0.0.1:9944",
+        "rpc_url": os.getenv("MADARA_RPC_URL", "http://127.0.0.1:9944"),
         "devnet": False,
         "check_interval": 6,
         "max_wait": 30,