Update optimisation class to return type dict

[BradyPlanden]

Feature description

The optimisation class should return type dictionary including the following:

• The parameter set with the identified or optimised values (linking to Update Parameter class to store and access multiple parameters #258)
• The optimisation variables (convergence for paramters and cost, optimisation type, number of iterations, etc.)
• If the forward model is pybamm based, the pybamm solution object.

Motivation

A dictionary object allows for all the relevant information from the optimisation to be stored in one object. This makes it easier for debugging and post-processing the optimisation solution.

Possible implementation

No response

Additional context

No response