Convert man zpool.8 to mdoc (OpenZFS sync)

* Fixed some typos
* Additional description for some commands arguments
* `listsnapshots` remained
* Text reworked to be in sync with OpenZFS
* Added Linux as .Os type
* Updated `zpool events` section.
* Updated `zpool iostat|status -c` sections
* Added zed(8) reference to SEE ALSO

Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: George Melikov <[email protected]>
Closes openzfs#6245