Generate Python bindings from OpenAPI spec

SOLR-16346 added support to Solr's build to generate an "OpenAPI spec" file describing our v2 API. But currently, this spec file isn't actually used by Solr in any way.

Spec files can be used for a variety of purposes, including to generate client bindings in a variety of languages.

OpenAPI supports client-generation in many languages. Among these Python is particularly promising due to the popularity of the language itself and of the 3rd-party "pysolr" client.

(It's also an appealing starting-point from a development perspective, as it's "green field" and therefore unconstrained by compatibility concerns as the Java binding in SOLR-16825 is.)