Support linehaul data in user agent

[konstin]

Issue Kind

Brand new capability

Description

Linehaul is a feature by PyPI that allows querying statistics about the used platforms through BigQuery (https://github.com/pypi/linehaul-cloud-function). Clients query the host environment and attach this information as a JSON blob in the User Agent header. https://github.com/pypi/linehaul-cloud-function/blob/main/linehaul/ua/datastructures.py provides an overview over the datastructure.

Impact

This information is extremely valuable to understand usage across platforms, Python versions, CI and what components can or can't assume to present on a target system. Both pip and uv send linehaul data, but it would be valuable to increase the coverage.

Workarounds

The data is biased towards pip and uv