Add to docs/alternator/new-apis.md a full description of the
`system.clients` support in Alternator that was added in the previous
patches.
Although arguably *all* Scylla system tables should work on Alternator
and do not need to be individually documented, I believe that this
specific table, is interesting to document. This is because some of
the attributes in this table have non-obvious and Alternator-specific
meanings. Moreover, there's even a diffence in what each individual
item in the table represents (it represents active requests, not entire
connections as in CQL).
While editing the system tables section of new-apis.md, this patch also slightly
improves its formatting.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>