Toucan-connectors

Fixed

- Export of the peakina Connector through `CONNECTOR_REGISTRY`.

Changed

- Added a new Connector: [Peakina](https://github.com/ToucanToco/peakina) for files.

Fixed

- Google Big Query no longer crashes when trying to retrieve the table list for datasets in different locations.

Changed

- `Dates as float` is now selected by default in Google Sheets data sources.

Changed

- Feat: The connector `GoogleSheets` datasource now has an option called `Dates as Floats`, to see date time columns as strings or float when reading the sheet.

Breaking changes

Pagination information has been refactored. The `DataSlice` and `DataStats` interfaces have been changed:

* `DataStats` no longer has `total_rows` and `total_returned_rows` fields.
* `DataSlice` now has a `pagination_info` field in its root. This field is required and contains a `PaginationInfo` model.

For information about the `PaginationInfo` model and how to interpret its contents, see the [documentation](doc/PaginationInfo.md).

Changed

- Deps: Upper constraint on cryptography has been loosened from <37 -> <39
- Snowflake: The snowflake connector has been refactored in order to prevent spawning threads
and connection pooling.