Allow using URL as archive source when creating functions (#1360)

In the case of large files, it takes a long time for the user to download
the source from the URL and upload it to StorgeSvc through CLI.

This PR allows a user to use URL as the function source when creating a function
and provides a new flag "--keeparchiveurl" to let the user to decided
whether the CLI should download the file first or store the file URL in the
archive directly. If "--keeparchiveurl" is true, then no checksum will be
generated, it's the user's responsibility to ensure the file won't be changed.

test/init_tools.sh

@@ -54,6 +54,14 @@ if [ $(uname -s) == 'Darwin' ]; then
         exit 1
     fi
 
+    if command -v gsha256sum >/dev/null; then
+        sha256sum() { gsha256sum "$@"; }
+        export -f sha256sum
+    else
+        echo '"gsha256sum" command not found. Try "brew install coreutils".'
+        exit 1
+    fi
+
     find_executable() {
         path=$1; shift
         find $path -perm +111 -type f "$@"