Enable swaps on Sepolia testnet (#3710)

As Goerli testnets becomes deprecated with end of 2023, we've been
migrating to another testnet - Sepolia. Up to this point we were not
able to support swaps there, as 0x did not support Sepolia. But recently
0x created theAPI endpoint for Sepolia, so we're now able to use their
services.
Read more: https://0x.org/docs/0x-swap-api/api-references/overview.

Tests:
- [x] Execute swap of a base asset on Ethereum Sepolia
- [x] Execute swap of an ERC-20 asset on Ethereum Sepolia
- [x] Make sure swaps are not available for Arbitrum Sepolia

Latest build:
[extension-builds-3710](https://github.com/tahowallet/extension/suites/19134730944/artifacts/1121134638)
(as of Mon, 18 Dec 2023 11:08:22 GMT).

background/constants/networks.ts

@@ -186,7 +186,7 @@ export const CHAIN_ID_TO_0X_API_BASE: {
   [POLYGON.chainID]: "polygon.api.0x.org",
   [OPTIMISM.chainID]: "optimism.api.0x.org",
   [GOERLI.chainID]: "goerli.api.0x.org",
-  // TODO: Add Swap API for Sepolia once 0x supports it.
+  [SEPOLIA.chainID]: "sepolia.api.0x.org",
   [ARBITRUM_ONE.chainID]: "arbitrum.api.0x.org",
   [AVALANCHE.chainID]: "avalanche.api.0x.org",
   [BINANCE_SMART_CHAIN.chainID]: "bsc.api.0x.org",