Run make to generate apidocs rst

Run the apidocs target in the already existing Makefile for generating
module API docs before the builtin build command to generate docs is
run.

.readthedocs.yaml

@@ -10,6 +10,12 @@ build:
   os: ubuntu-22.04
   tools:
     python: "3.9"
+  apt_packages:
+    - make
+  jobs:
+    pre_build:
+      # generate API reference docs .rst files from module source
+      - make -C docs/ apidocs
 
 # Build documentation in the docs/ directory with Sphinx
 sphinx: