SE-3082: Add custom transactions using custom properties notebook

[dgbarclay]

Pull Request Checklist

• [x] Changes follow the style guide
• [x] Tests pass
• [x] Raised the PR against the develop branch

Description of the PR

This notebook shows how to create custom transaction types that pass reference values (units, instruments, exchange rates) from custom transaction properties into the Movements Engine. This means that it is possible to upsert transactions that do not use the standard transaction fields as points of reference, as such, providing a solution for bespoke transactions fields that better represent a user's interpretation of some transaction types, e.g. FX transactions.

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[adamMQM]

/LGTM