Transaction support #18
Description
An earlier version of Herda server included support for transactions built into database models, but this was removed because transactions aren't actually supported in a single node arrangement, which is the standard development environment.
In place of that support, an optional ClientSession parameter has been introduced instead to various model functions, which if set automatically attaches all queries to a transaction. This is better anyway for enabling several models to use the same transaction, which can be created and committed/aborted at the call site - typically an API handler.
However, none of the API handlers currently make use of the extra parameter.
It will be useful to officially add support for transactions, enabling more robust database management in a cluster environment. This will of course need a cluster environment to be set up to be tested properly.