feat(connector-corda): support Release 4.8

[petermetz]

At the time of this wriging Corda 4.8 is about to drop. We don't know when exactly, but make sure to check if it's out yet before taking on this issue to be worked on.

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Description

The connector should support 4.8. It most likely already does, but we need actual test coverage and the AIO image updated for said test coverage so that we can credibly claim said support instead of just saying "well it should because I read the release notes of Corda 4.8 and nothing struck me as a breaking change that would mess with our connector".

Acceptance Criteria

1. Specific test case that is locked down to a 4.8 ledger (the AIO image) so that even if we add more things later on, this test remains frozen in time forever verifying the connector against 4.8.
2. Will probably have to make sure an updated version of the Corda AIO image is published because right now it can only do Corda 4.6 IIRC

cc: @takeutak @sfuji822 @hartm @jonathan-m-hamilton @AzaharaC @jordigiam @kikoncuo @petermetz @arnab-roy