like envoy doc configured, use pathSeparatedPrefix and pre_rewrite is "/":

the pathSeparatedPrefix "/om/backend" would watch

• /om/backend
• /om/backend/
• /om/backend/v1
• /om/backend?param=true

reference envoy docs:

but the upstream receive double "/"

the pre_rewrite is not "/" work fine:

I think we should trim the double "/" when the prefix_write is "/" and the prefix is pathSeparatedPrefix.