Show the default version of built-in (Python) tools in docs somewhere

[huonw]

Describe the bug

Currently the default version of a Python tool built-in to Pants (like black) doesn't seem to be shown in the documentation anywhere, it's just implied by the lockfile, which is hidden: e.g. https://www.pantsbuild.org/2.19/reference/subsystems/black

(Compare a JVM tool like openapi-generator which has a default value for the version field: https://www.pantsbuild.org/2.19/reference/subsystems/openapi-generator#version)

This leads to confusion when newer releases of a tool change behaviour, deprecate options or even introduce new ones (like #20707) and a user can't tell why their configuration isn't working when run with Pants.

Suggestion: have PythonToolRequirementsBase dynamically argument the subsystem's help text by reading the lockfile. For instance, for the page above, adding the second paragraph in:

The Black Python code formatter (https://black.readthedocs.io/).

This version of Pants uses Black 23.3.0 by default. Use a dedicated lockfile and the install_from_resolve option to control this.

This could potentially also be applied to the install_from_resolve and/or requirements fields.

Pants version
2.19

OS
N/A

Additional info
N/A

[krishnan-chandra]

Happy to take this one! Assigned to myself