Remove the Unnecessary inflexibility in building the sampler

[odunbar]

Currently the get_obs function with build=true, creates a vector with a length based on the first observation, rather than requesting each observation in turn - this is a simple fix that will allow different sized minibatchers

EnsembleKalmanProcesses.jl/src/Observations.jl

Lines 790 to 791 in 0c742b0

	sample_length = length(get_obs(observations_vec[1], build = true))
	minibatch_samples = zeros(sample_length * minibatch_length)