add Databricks db support

[leo-schick]

This PR adds support for Databricks including

• shell query_command and copy_to_stdout_command via dbsqlcli, pypi package databricks-sql-cli
• cursor via mara_db.databricks.databricks_cursor_context using pypi package databricks-sql-connector
• sqlalchemy support via pypi package sqlalchemy-databricks

Open tasks

• add rtd documentation
• update Readme.md
• testing the implementation

[leo-schick]

Hi @alexeyegorov,
in case you still use Mara somewhere, are you interested to do a review of this PR? This PR adds Databricks support for Mara. This might be helpful to you when you still have some legacy mara pipelines you want to migrate to Databricks.

Note that reading data from STDIN via mara_db.shell.copy_from_stdin_command is not supported yet. This means the commands ReadFile, ReadSQLite and Copy from mara_pipelines are not supported. But you can do a woraround by writing the data to a data lake and then use a unmanaged table or COPY INTO in databricks.

[alexeyegorov]

Hey Leo!
I am so sorry. I have also missed your other request. Let me get back on that tomorrow or better on Monday!
We are currently migrating to Databricks completely and had a lot of work to do. Mara will be used for some more months still and maybe this MR is really an interesting one. ;)

[alexeyegorov]

So basically it looks good. I will forward this again to our team and discuss if we could also use this feature as we are switching to Databricks completely, but maybe it can help us on the transition.