exp: basic hydra sweeper support

[dberenbaum]

Hydra also allows for running hyperparameter sweeps. Using Hydra, the same could be supported in DVC (see https://hydra.cc/docs/intro/#multirun):

$ dvc exp run --set-param train=random_forest,gradient_boosting

Originally posted by @dberenbaum in https://github.com/iterative/dvc/discussions/7044#discussioncomment-3271855