Release to Main

[acwooding]

Features

• Add copy_dataset as a built in transformer function
• Add new helper functions in helper.py:
  • dataset_from_fsurl: Create a dataset from the contents of an fsspec URL
  • metadata_from_fsurl: Create metadata, FILESET file list from fsspec URL
  • derived_dataset: Create a derived dataset via a single function call on .data from a
    previous dataset
• Add support for using arbitrary conda channels in the environment.yml while forcing the order the channels getting added using a channel-order section (coming in Extend environment management to handle arbitrary conda channels #245)

API Changes

• .DESCR -> .README
• .EXTRA -> .FILESET

Documentation Updates

• Update docs to be more clear and concise
• Re-add process_20_newsgroups as a working example of a process function

Tests

• Use a miniconda image directly instead of python image and installing miniconda on it
• Fix docstring tests in _paths.py