Adds Databricks backend

[edgararuiz]

Test results:

 pins-python % pytest pins -m 'fs_dbc' -v   
===== 56 passed, 6 skipped, 418 deselected in 967.27s (0:16:07) ========

Overview:

Following the same pattern for Posit Connect, it adds a "stub" fsspec spec to create the integration. It uses databricks-sdk to authenticate and interact with Databricks.

Details:

• Adds board_databricks() function that follows the same pattern of the other boards
• Adds a new AbstractFileSystem (fsspec) named DatabricksFs, which is called by the board constructor, just like it does with Posit Connect boards
• DatabricksFs overrides ls, exists, open, get, mkdir, get, put and rm
• Adds new BoardBuilder for testing. DbcBoardBuilder overrides __init__, create_tmp_board, teardown_board, and teardown

[isabelizimm]

There are a few methods that don't need to be staticmethod (anything that uses self won't need a staticmethod decorator), but apart from that this looks good!

FYI that the failing tests are unrelated-- I have a few pieces of maintenance that I'll need to merge before this can go in.

[isabelizimm]

Due to some boring housekeeping reasons, our test boards are all read-only right now for Databricks. That means things we test a few things like pin_read and pin_list but do NOT test pin_write and many other functionalities.

I've added this decorator + lots of TODOs to note all the tests we are skipping on dbc 😬 We'll release this as-is for now, but plan to change to make this fully tested in the future.