Allow users to specify hyperparameter priors

[BradyPlanden]

Feature description

Allow for users to provide a prior on the cost hyper-parameters when they are included within the optimisation/sampling process. This is currently a fixed prior located:

PyBOP/pybop/builders/pybamm.py

Line 112 in 347c94c

delta = obj.default_value * 0.5 # Create prior w/ large variance

Motivation

No response

Possible implementation

No response

Additional context

No response