Add Ability to Set client_max_size for Webhook Server

[wip-abramson]

Work has been undertaken in ACA-Py to explore supporting credential issuance for large creds 1 < 16Mb.

The current default for an aiohttp web.Application() is to support 1Mb max client request size. ACA-Py have added this additional config arg to change this on the agent https://github.com/hyperledger/aries-cloudagent-python/blob/68347f8e1f3b918464019bdc2d891926de023f5c/aries_cloudagent/config/argparse.py#L164

For our webhook server to receive and process events from an agent processing messages of this size, we would need to support somewhere in the order of 4x the credential size. This data gets represented multiple times in the webhook payload by the time the protocol gets into the credential_acked state.

For now we could just add an optional argument to specify the client_max_size when initialising the webhook?

[TimoGlastra]

Not relevant anymore