Add python version search script

tools/get-best-python-for-docs-build.sh

@@ -0,0 +1,33 @@
+#!/usr/bin/env bash
+
+# This script prints the version suffix of the most suitable version of Python
+# for building docs that's installed in this system.
+#
+# Caller can safely append this suffix to `python` or `pip` and expect the
+# binary to exist.
+#
+# If no usable version of Python is available, this script will exit with a
+# non-zero code.
+
+set -e
+
+# if `python3` is >= 3.8 and `pip3` is available, use that
+if echo -e "import sys\nif sys.version_info < (3,8):\n exit(1)" | python3 && \
+which pip3 1>/dev/null 2>&1; then
+    echo "3"
+    exit 0
+fi
+
+# check `python3.N` from newest to oldest
+CANDIDATE_SUFFIXES=("3.11" "3.10" "3.9" "3.8")
+for SUFFIX in ${CANDIDATE_SUFFIXES[@]}; do
+    # if both `python3.N` and `pip3.N` are available, use that
+    if which "python$SUFFIX" 1>/dev/null 2>&1 && \
+    which "pip$SUFFIX" 1>/dev/null 2>&1; then
+        echo "$SUFFIX"
+        exit 0
+    fi
+done
+
+# none found
+exit 1