fix: rename das module to sampler, or figure out naming for da module

[distractedm1nd]

Context:

          I am OK with calling this da if we change `das` to `sampler` or smlr. Changing, this shouldn't be part of this PR, but we should at least have an issue to clean this ambiguity after this is merged

Originally posted by @Wondertan in https://github.com/celestiaorg/celestia-node/issues/3146#issuecomment-1921574151

[ramin]

i like renaming das -> sampler personally