Create a test Cardano transactions builder

[jpraynaud]

Why

We need to have a simple and versatile way of creating test transactions which are used in our unit tests. We have already created multiple generators in the code that will be superseded by this builder. The builder will be tested which will allow better quality of tests.

What

Assess the existing generators and implement a builder that will fit all the existing needs and which can be easily extended with new needs.

How

• Assess the existing generators (Focus on the generator in the prover service)
• Design and implement a transactions builder