Processing toolbox: Add option to `generate bounding boxes` of features

[arjxn-py]

https://docs.qgis.org/3.40/en/docs/user_manual/processing_algs/qgis/vectorgeometry.html#qgisboundingboxes

Add an option in processing toolbox that creates bounding box geometries (envelopes) for each feature in a vector layer. This can be useful for visualizing the spatial extent of features.

This operation would:

• Replace each geometry with a rectangle (its bounding box).
• Preserve the original feature attributes.

A simple ogr2ogr command would look like:

[
  '-f', 'GeoJSON',
  '-dialect', 'sqlite',
  '-sql', 'SELECT ST_Envelope(geometry) AS geometry, * FROM input'
]

[arjxn-py]

Demo for reference:

Screen.Recording.2025-06-05.at.14.37.13.mp4

[arjxn-py]

Done in #744