MAINTAINERS: supplement of zswap maintainers update

MAINTAINERS: supplement of zswap maintainers update

As discussed on the mailing list [1], merge the zpool maintainers entry
into the zswap one.  Also, add CREDITS entries for previous zswap/zpool
maintainers.

[1] https://lore.kernel.org/linux-mm/CAJD7tkYx4YWhGoVwnSeGc8dY_1aRRxxg8PzWBV==A6iqG_OgFw@mail.gmail.com/

Link: https://lkml.kernel.org/r/20240117182152.1439822-1-yosryahmed@google.com
Signed-off-by: Yosry Ahmed <yosryahmed@google.com>
Acked-by: Nhat Pham <nphamcs@gmail.com>
Acked-by: Dan Streetman <ddstreet@ieee.org>
Acked-by: Seth Jennings <sjenning@redhat.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Vitaly Wool <vitaly.wool@konsulko.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>