expose progress bar print rate option in MCMC

[mdmould]

Allows a user input print_rate to numpyro.infer.MCMC to set the number of iterations per progress bar update.

This was motivated by wanting to have more frequent progress bar update for slow iterations when num_chains>1, where the default was to update after each 5% of total iterations, but it also works for num_chains=1.

[Qazalbash]

Thanks @mdmould

[Qazalbash]

@mdmould CI is failing on lint and formatting. Please run prek run -a or pre-commit run -a and push the new changes.

[mdmould]

My bad, just ran and pushed