Propose lambda from a gamma conditional conjugate posterior proposal
.lambda_conj_prop(df, beta, j, bp, alam = 0.01, blam = 0.01)list containing proposed lambda, shape and rate parameters
data.frame from dataframe_fun()
parameter value for beta
current split point
number of covariates
lambda hyperparameter, default set to 0.01
lambda hyperparameter, default set to 0.01