Allow external_id to be set during ingestion

[ian]

We have a need for our local DB's document IDs to match those in Morphik.

This allows for a metadata external_id property to be set which overrides the default document UUID generator.

[prophet-code-review-bot]

Bug Report

Name	Severity	Example test case	Description
Inconsistent Handling of external_id after pop	High	Upload a file with external_id in metadata and verify it is not present in the document's metadata but is present as a separate field. Check if the system relies on external_id being present in both places.	The code uses metadata_dict.pop("external_id", None) which removes the external_id from the metadata_dict. This might be incorrect if the system relies on the external_id being present in both the dedicated external_id field and within the metadata dictionary.
Missing Handling of Empty Metadata	Low	Upload a file with only external_id in the metadata.	If the metadata_dict is empty after popping the external_id, the code might behave unexpectedly in downstream processes that rely on the metadata.

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[cubic-dev-ai]

mrge reviewed 1 file and found no issues. Review this PR in mrge.io.

[prophet-code-review-bot]

Bug Report

Name: external_id parameter in ingest_text function call incorrect.
Severity: High
Example test case: Call the /ingest_text endpoint, providing a value for the external_id parameter. The document created will not have that external_id.
Description: In core/services/document_service.py, the ingest_text function definition includes the external_id parameter, however, when calling the Document constructor, the external_id argument is being passed in incorrectly. external_id=external_id if external_id else None, does not pass the value, so it is being passed as a boolean expression instead of the value of external_id. This means the external_id is never set.

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