Add script for downloading a branch or tag of sdm_schemas

docker/scripts/download-sdm-schemas.sh

@@ -0,0 +1,25 @@
+#!/bin/bash
+
+_url=https://github.com/lsst/sdm_schemas.git
+
+# Make sure SDM_SCHEMAS_REF is set with default
+if [ -z "$SDM_SCHEMAS_REF" ]; then
+    SDM_SCHEMAS_REF=main
+fi
+
+echo "Cloning SDM schemas from $_url at $SDM_SCHEMAS_REF"
+
+# Determine if SDM_SCHEMAS_REF is a branch or a tag
+if git ls-remote --heads "$_url" "$SDM_SCHEMAS_REF" | grep -q "$SDM_SCHEMAS_REF"; then
+    echo "$SDM_SCHEMAS_REF is a branch"
+    git clone --depth=1 --branch "$SDM_SCHEMAS_REF" "$_url"
+elif git ls-remote --tags "$_url" "$SDM_SCHEMAS_REF" | grep -q "refs/tags/$SDM_SCHEMAS_REF"; then
+    echo "$SDM_SCHEMAS_REF is a tag"
+    git clone --depth=1 "$_url"
+    pushd sdm_schemas
+    git checkout tags/"$SDM_SCHEMAS_REF"
+    popd
+else
+    echo "Error: $SDM_SCHEMAS_REF is neither a branch nor a tag."
+    exit 1
+fi