gnu: Add python-prometheus-client.

* gnu/packages/python-xyz.scm (python-prometheus-client): New variable.

Co-authored-by: Marius Bakke <mbakke@fastmail.com>

gnu/packages/python-xyz.scm

@@ -18878,3 +18878,25 @@ (define-public python-pymacaroons
 simple and fast to verify, and decouple authorization policy from the
 enforcement of that policy.")
     (license license:expat)))
+
+(define-public python-prometheus-client
+  (package
+    (name "python-prometheus-client")
+    (version "0.7.1")
+    (source
+     (origin
+       (method url-fetch)
+       (uri (pypi-uri "prometheus_client" version))
+       (sha256
+        (base32 "1ni2yv4ixwz32nz39ckia76lvggi7m19y5f702w5qczbnfi29kbi"))))
+    (build-system python-build-system)
+    (arguments
+     ;; TODO: No tests in the PyPI distribution.
+     `(#:tests? #f))
+    (propagated-inputs
+     `(("python-twisted" ,python-twisted)))
+    (home-page "https://github.com/prometheus/client_python")
+    (synopsis "Prometheus instrumentation library")
+    (description
+     "This is the official Python client for the Prometheus monitoring server.")
+    (license license:asl2.0)))