Show warning message if `initial_parameters` is passed instead of `initial_params`

See, https://github.com/TuringLang/DynamicPPL.jl/pull/1057#issuecomment-3351035212 and [commit](https://github.com/TuringLang/DynamicPPL.jl/pull/1057/commits/235068ba202863ea3a8bde6bf76ae2b869c85600)