[RLlib] Deprecate get_algorithm_class().

[sven1977]

Signed-off-by: sven1977 svenmika1977@gmail.com

Deprecate get_algorithm_class().
In favor of ray.tune.registry.get_trainable_cls()

algo_cls, config = get_algorithm_class("[some name]", return_config=True)
->
algo_cls = get_trainable_cls("[some name]"); config = algo_cls.get_default_config();

algo_cls = get_algorithm_class("[some name]", return_config=False)
->
algo_cls = get_trainable_cls("[some name]")

Why are these changes needed?

Related issue number

Checks

• I've signed off every commit(by using the -s flag, i.e., git commit -s) in this PR.
• I've run scripts/format.sh to lint the changes in this PR.
• I've included any doc changes needed for https://docs.ray.io/en/master/.
• I've made sure the tests are passing. Note that there might be a few flaky tests, see the recent failures at https://flakey-tests.ray.io/
• Testing Strategy
  • Unit tests
  • Release tests
  • This PR is not tested :(

[ArturNiederfahrenhorst]

lgtm!

[ArturNiederfahrenhorst]

though tests are failing due to some recursion issue.

[ArturNiederfahrenhorst]

I've added a commit that resolves the circular calls

[ArturNiederfahrenhorst]

.. and these fixes are simple ones for the few failing tests.

[ArturNiederfahrenhorst]

lgtm!