This release:
- Updates the folder structure for user imports (more below).
- Fixes a few hiccups with serialization and registration
- Removes the requirements that `pyflyte` had on the `--config` value. This makes the out-of-container serialization process a bit simpler. Users should still use a config file if tasks depend on multiple images. See [cookbook](https://flytecookbook.readthedocs.io/en/latest/auto_core_intermediate/multi_images.html).
Depending on the way your flytekit imports were listed, this release may be a breaking change. All parts of flytekit that both users and contributors would need to use have hopefully been moved into one of three `__init__.py` files. For example, please see the changes we had to make to our example [cookbook repo](https://github.com/flyteorg/flytesnacks/pull/99/files#diff-99f0537085255065252c64e216bc70594300109963b6850db81df6b49d0e7f1cR41).
* `flytekit/__init__.py` This is the main place users should be importing from and contains the necessary imports to take advantage of the nominal Flyte platform. This is where you'll find things like the `task` and `workflow` decorators, as well as the various notification types, etc.
* `flytekit/testing/__init__.py` Currently this just has two functions, `task_mock` and `patch`, used to override task execute behavior and is needed to mock out tasks that don't run locally (like a Hive task) when unit testing workflows.
* `flytekit/extend/__init__.py` This file exposes some of the internals of flytekit used when extending the sdk. As a reference, please see the various plugins in the `plugins/` folder at the top layer of this repo. Note: in the [separation of plugins change](https://github.com/flyteorg/flytekit/pull/339), we had neglected to formally separate out the raw flytekit dependencies. That is, [`spark/task.py`](https://github.com/flyteorg/flytekit/blob/master/plugins/spark/flytekitplugins/spark/task.py) for example, the `flytekit` imports were not from one of the three sub-packages listed above, and went into the `annotated` package directly. This PR also fixes that.