Python: (Astra DB) Explicit projection when reading from Astra DB

[hemidactylus]

Motivation and Context

In view of upcoming changes in the Astra DB Data API, this PR explicitly sets a projection every time a find command is executed, in order to ensure all necessary fields of the document are returned by the API.

Description

Added an else branch in the astra_client.py to ensure there always is a "projection" field in the body for the find command. This ensures that $vector is returned by the API even in case of Astra DB rolling out an exclude-it-by-default policy in the future.

Contribution Checklist

• [x] The code builds clean without any errors or warnings
• [x] The PR follows the SK Contribution Guidelines and the pre-submission formatting script raises no violations
• [x] All unit tests pass, and I have added new tests where possible
• [x] I didn't break anyone :smile: