get_pm_kernel: Get pseudo-marginal random walk Metropolis-Hastings kernels
In lolmid/unbiased_intractable_targets: Debiased particle MCMC with couplings

This function takes descriptions of the target and tuning parameters, and returns a list containing the keys single_kernel, coupled_kernel corresponding to marginal and coupled pseudo marginal kernels, with Normal random walks. These kernels can then be used in the function coupled_chains.

1 2	get_pm_kernel(logtarget, state_crn_sample, latent_state, Sigma_proposal, dimension)

`logtarget`	function to compute target log-density, e.g. see `get_mvnormal`
`latent_state`	function to transform the random numbers into samples of the latent state
`Sigma_proposal`	variance of the Normal random walk for the proposals
`dimension`	dimension of the target distribution
`state_crn_sampe`	function to sample the random numbers used to estimate the target