Until now we set metadata value pointers into the onward wsi ah data
area... that's OK until we get a situation the wsi has gone away before we
have a chance to deliver the metadata over the proxy link.
Add a variant lws_ss_alloc_set_metadata() that allocates space on the heap
and takes a copy of the input metadata. Change ss-h1 to alloc copies of
its metadata so we no longer race the wsi ah lifetime.
