fix: update apidiff script to install tool and set up remote repository

Author: yongruilin

Diff for: .gitignore

@@ -1 +1 @@
-.idea
+.idea

Diff for: hack/apidiff.sh

@@ -24,7 +24,7 @@ usage() {
     echo "   -t <revision>: Report changes in code up to and including this revision."
     echo "                  Default is the current working tree instead of a revision."
     echo "   -r <revision>: Report changes in code added since this revision."
-    echo "                  Default is the common base of origin/master and HEAD."
+    echo "                  Default is the common base of master and HEAD."
     exit 1
 }
 
@@ -53,16 +53,39 @@ if [ "$#" -ge 1 ]; then
     TARGET_DIR="$1"
 fi
 
+# Ensure LOCAL_GOBIN is an absolute path
+LOCAL_GOBIN="$(pwd)/_output/bin"
+mkdir -p "${LOCAL_GOBIN}"
+
+# Add cleanup trap to remove the temporary binary directory
+trap 'rm -rf "${LOCAL_GOBIN}"' EXIT
+
 # Check for apidiff tool, install it if not found
 if ! command -v "${API_DIFF_TOOL}" &> /dev/null; then
+    GOBIN=${LOCAL_GOBIN}
     echo "Installing apidiff into ${GOBIN}."
-    go install golang.org/x/exp/cmd/apidiff@latest
+    GOBIN=${LOCAL_GOBIN} go install golang.org/x/exp/cmd/apidiff@latest
+    # Add GOBIN to PATH
+    export PATH=$PATH:${GOBIN}
 fi
 
 # Fetch common base if -r is not set
 if [ -z "${REFERENCE_REVISION}" ]; then
-    echo "Determining common base with origin/master..."
-    REFERENCE_REVISION=$(git merge-base origin/master HEAD)
+    # First try using Prow environment variables
+    if [ -n "${PULL_BASE_SHA:-}" ] && [ -n "${PULL_PULL_SHA:-}" ]; then
+        echo "Using Prow environment variables to determine base revision..."
+        if ! REFERENCE_REVISION=$(git merge-base "${PULL_BASE_SHA}" "${PULL_PULL_SHA}"); then
+            echo "Error: Failed to detect base revision using Prow environment variables." >&2
+            exit 1
+        fi
+    else
+        # Fall back to upstream/master
+        echo "Determining common base with upstream/master..."
+        if ! REFERENCE_REVISION=$(git merge-base upstream/master HEAD); then
+            echo "Error: Could not determine base revision. Please set -r explicitly." >&2
+            exit 1
+        fi
+    fi
 fi
 
 # Step 1: Create a temporary directory for worktrees