scripts/prepare-release: option to only create assets

Add '-a' command line option to only create release assets and not patch
any files in the repo. E.g.

  $ scripts/prepare-release.sh -a v0.8.0+1 user@example.com

scripts/prepare-release.sh

@@ -9,6 +9,7 @@ Usage: $this [-h] RELEASE_VERSION GPG_KEY
 
 Options:
   -h         show this help and exit
+  -a         only generate release assets, do not patch files in the repo
 
 Example:
 
@@ -33,8 +34,11 @@ files:
 #
 # Parse command line
 #
-while getopts "h" opt; do
+assets_only=
+while getopts "ah" opt; do
     case $opt in
+        a)  assets_only=y
+            ;;
         h)  usage
             exit 0
             ;;
@@ -79,6 +83,7 @@ else
     exit 1
 fi
 
+if [ -z "$assets_only" ]; then
     # Patch docs configuration
     echo Patching docs/_config.yml
     sed -e s"/release:.*/release: $release/"  \
@@ -107,6 +112,7 @@ echo Patching test/e2e/node_feature_discovery.go flag defaults to k8s.gcr.io/nfd
     sed -e s'!"nfd\.repo",.*,!"nfd.repo", "k8s.gcr.io/nfd/node-feature-discovery",!' \
         -e s"!\"nfd\.tag\",.*,!\"nfd.tag\", \"$release\",!" \
       -i test/e2e/node_feature_discovery.go
+fi
 
 #
 # Create release assets to be uploaded