feat(gcloud): add Mac M1 Homebrew path (#10143)

Homebrew on Mac M1 is moved to the /opt/Homebrew location. This change updates the search
locations with this path.

plugins/gcloud/gcloud.plugin.zsh

@@ -7,6 +7,7 @@ if [[ -z "${CLOUDSDK_HOME}" ]]; then
   search_locations=(
     "$HOME/google-cloud-sdk"
     "/usr/local/Caskroom/google-cloud-sdk/latest/google-cloud-sdk"
+    "/opt/homebrew/Caskroom/google-cloud-sdk/latest/google-cloud-sdk"
     "/usr/share/google-cloud-sdk"
     "/snap/google-cloud-sdk/current"
     "/usr/lib64/google-cloud-sdk/"