MINOR: [Dev][Release] Stop post-04-website.sh script if archery isn't…

… available (apache#44823)

### Rationale for this change

The release script at `dev/release/post-04-website.sh` doesn't quite work right if archery isn't available. The PR gets made but the changelog isn't included. See when this happened during the 18.0.0 release: apache/arrow-site#551 (comment). 

### What changes are included in this PR?

Before the script does anything meaningful, it checks for archery and stops if it's not available.

### Are these changes tested?

Yes.

### Are there any user-facing changes?

No.

Lead-authored-by: Bryce Mecum <petridish@gmail.com>
Co-authored-by: Sutou Kouhei <kou@cozmixng.org>
Signed-off-by: Sutou Kouhei <kou@clear-code.com>

dev/release/post-04-website.sh

@@ -29,6 +29,12 @@ if [ "$#" -ne 2 ]; then
   exit 1
 fi
 
+# Verify archery is available and stop if not
+if ! archery --help > /dev/null 2>&1; then
+  echo "This script requires archery. Please install it and try again."
+  exit 1
+fi
+
 previous_version=$1
 version=$2