Add Sepolia-related external contracts

Adding Sepolia-related contracts needed for deployment on `amoy` network:
* `external/baseSepolia/BaseTokenBridge.json` - address taken from
  https://docs.wormhole.com/wormhole/blockchain-environments/evm#testnet-contracts-base-sepolia-84532
* `external/amoy/SolanaWormholeGateway.json` - used the same value as in `mumbai`
* `external/sepolia/TokenBridge.json` - address taken from
  https://docs.wormhole.com/wormhole/blockchain-environments/evm#testnet-contracts-sepolia-11155111

NOT included in this commit (but needed for the deployment):
* `external/amoy/PolygonWormholeTBTC.json` - in order to get the address we need
  to perform attestation of the Ethereum Sepolia TBTC token on Amoy (but atm
  Amoy is not available on the list of target networks on
  https://wormhole-foundation.github.io/example-token-bridge-ui/#/register)
* `external/amoy/PolygonTokenBridge.json` - address needs to be taken from
  https://docs.wormhole.com/wormhole/blockchain-environments/evm once Wormhole
  adds a support for Amoy

cross-chain/polygon/external/amoy/SolanaWormholeGateway.json

@@ -0,0 +1,3 @@
+{
+  "address": "0x69a22dc2e01ecd2ae40864822d4406ff8aed4e2b8932385dabe818422ff67e1b"
+}

cross-chain/polygon/external/sepolia/TokenBridge.json

@@ -0,0 +1,3 @@
+{
+  "address": "0xDB5492265f6038831E89f495670FF909aDe94bd9"
+}