Enhance the .append() function to support appending attachments

[DanaAbumourhMAG]

Request:
Enhance the arcgis.features.FeatureLayer.append() and arcgis.features.Table.append() functions in ArcGIS API for Python to support appending attachments along with features, improving efficiency of bulk attachments addition for large datasets.

Current Limitations:

• While ArcPy's arcpy.management.Append() supports appending attachments when setting the Maintain Attachments Environment setting to True, it does not preserve Global IDs when appending to hosted feature layers, even if setting the Preserve GlobalIDs Environment setting to True - See BUG-000133544's additional information.
• arcgis.features.FeatureLayer.append() does not support appending attachments and the Append REST API does not have that parameter.
• Alternative methods (edit_features() and AttachmentManager.add()) allow adding attachments but are inefficient for large datasets. 
• Esri’s documentation recommends using append() over edit_features() for large edits (250+ records), yet append() lacks attachment support.

Justification:

• Efficient bulk appending of both features and attachments is needed.
• Current workaround adding attachments (edit_features() and AttachmentManager.add()) after appending features) is inefficient for large datasets.
• Aligning append() with Esri’s own performance recommendations would improve usability.

Note: Found the following related questions about this subject in Esri Community:

• ArcGIS API for Python Append Does not Maintain Att... - Esri Community
• Solved: Copy attachments from one feature layer to another - Esri Community

[Clubdebambos]

This would be a great enhancement. 

It would be nice to be able to use upsert when appending and for attachments to be added if that attachment name is not already associated with the feature.