Cognite-sdk

Added
- added support for nonce authentication on transformations

Changed
- if no source or destination credentials are provided on transformation create, an attempt will be made to create a session with the CogniteClient credentials, if it succeeds, the acquired nonce will be used.
- if OIDC credentials are provided on transformation create/update, an attempt will be made to create a session with the given credentials. If it succeeds, the acquired nonce credentials will replace the given client credentials before sending the request.

Added
- added the sessions API

Removed
- Unused cognite.client.experimental module

Changed
- Helper functions for conversion to/from datetime now warns on naive datetimes and their interpretation.
Fixed
- Helper function `datetime_to_ms` now accepts timezone aware datetimes.

Fixed
- fixed missing README.md in package

Changed
- Poetry build, one single package "cognite-sdk"
- Require python 3.8 or greater (used to be 3.5 or greater)
Removed
- support for root_asset_id and root_asset_external_id filters. use asset subtree filters instead.