Should be passing an RNG here, not just a seed

[odunbar]

EnsembleKalmanProcesses.jl/src/EnsembleKalmanProcess.jl

Line 354 in 3e7494e

rng_seed::Union{IT, Nothing} = nothing,

Just noticed that we pass in a seed here, this should be passing around an rng::AbstractRNG so users can use more stable options than Random.seed!().

In particular we should be writing functions that take in
function f(..., rng::RNG) where {RNG <: AbstractRNG}
Or have a keyword with default
function f(..., rng = Random.default_rng())

and the rng should be stored in the ekp object.

This will make randomness far more traceable in our code.

[costachris]

Will be addressed in #281