In `testgen-hs`, print default embedded `protocol-params.json`, and allow changing them

[michalrus]

Context

By default we embed protocol parameters for Preview:

https://github.com/input-output-hk/testgen-hs/blob/7d58736ed578a9ccf8337376b302bb188b74303f/testgen-hs/protocol-params-preview.json

We then use them in the tests evaluating execution units.

It would be useful to:

1. Be able to print the default embedded protocol params from the final executable (that we release).

2. Be able to provide different protocol params to test evaluating execution units on different network configurations.

[michalrus]

/cc @ginnun

[ginnun]

My changes will allow setting this params while initializing the testgen-hs for streaming usage.

[michalrus]

Oh, nice! So I'll re-assign to you