fix: Send entire JSON, to send the Content-Length header [DAT-818]

[kittylon]

Summary

Sending data as generators does not set the Content-Length header in the POST request, which is required by the Tinybird /v0/datasources endpoint. Hence, calling the method append_ndjson throws the following error:
Already reported by @Pive01 in this Slack thread.

[ERROR] ApiError: API Error (411): Add a valid Content-Length header containing the length of the message-body. Documentation: https://docs.tinybird.co/api-reference/api-reference.html#limits

Extra considerations:

• All data sources do not get more than 100 records per day
• The GitHub API caps the commit difference to 250 [1]
• The /v0/datasources endpoint limit is at 5 times per minute [2]

Since we receive few records to iterate over, it makes sense to keep sending data in batches via the /v0/datasources endpoint. Once more data flows, we can consider the usage of the /v0/events endpoint + generators.

[thrau]

LGTM! even though i did really like the iterator pattern 😁

thanks for fixing this so quickly and adding the test!