Add custom paymaster handler config to react setup & hooks

[coffeexcoin]

We can't currently use a custom paymaster handler with react hooks (createSession, useWriteContractSponsored, etc...).

For example here - these hooks are using the global AbstractWalletProvider but there is currently no way to set customPaymasterHandler on the client in this scenario.

• Update the global context in agw-react to allow passing a custom paymaster handler in config such that any AGW client being configured will use the custom paymaster handler.
• Update custom react hooks that create an agw client to allow an override custom paymaster handler to be passed in