Add Fisher Information Matrix function

[matheusaps]

Hello Distributions.jl team,

I'm writing to propose adding a function to Distributions.jl to calculate the Fisher Information Matrix (FIM) for distributions.

The FIM is crucial for statistical inference, offering insights into parameter uncertainty, in addition to being part of the definition of score-driven models. Integrating this functionality would increase the usefulness of the package and increase its value to users.

Thank you for considering this proposal.

Yours sincerely,