Don't raise exception when closing a stale Thrift session

[susodapop]

Prior to this change, if a context manager or a user explicitly called Connection.close() twice on the same connection, the second call would raise an exception:

databricks.sql.exc.DatabaseError: Invalid SessionHandle: SessionHandle [<GUID>]

This sometimes affects dbt, airflow and others if they use connections as a context manager.

This pull request explicitly catches this error, logs it cleanly, and then continues execution. The pull request is broken into a few commits that do this:

1. Make it easy to see log messages when running pytest
2. Implement a method that converts the bytes session_handle we receive from Thrift server into a human readable GUID
3. Explicitly catch the InvalidSession handle error (this is the most important part of this PR)
4. Log when this happens so we can observe it (this shouldn't happen in the normal course of usage)
5. Update the changelog
6. Unrelated: update test.env.example to include the environment variables we need for running sqlalchemy e2e tests. This is just convenient. Has no impact on the connector as installed for users.

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[jadewang-db]

wondering if we should swallow all exceptions for close session calls.

[susodapop]

Good thought. I've updated the code to log all exceptions but not raise them.

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[susodapop]

Oddly, my integration test that I added is now failing. Researching before I merge this...

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[susodapop]

Okay I researched why it failed. It's because the Databricks thrift server no longer raises an exception upon multiple attempts to emit closeSession for the same handler. I've revised my test to account for this and updated the logging.