pd(generate): use constants from penumbra_app

[erwanor]

Describe your changes

pd network generate and the application use consensus parameters defined in two different places which is confusing and error-prone.

This PR makes pd network generate import constants from the app.

Checklist before requesting a review

• If this code contains consensus-breaking changes, I have added the "consensus-breaking" label. Otherwise, I declare my belief that there are not consensus-breaking changes, for the following reason:

This only affects new runs of pd network generate.

[conorsch]

Refs #4627, #4614.

[conorsch]

Great find, @erwanor! Adding the constants was clutch, and using them where they're needed is even better.