REST: Add new setting for maximum API page size

REST: Add new setting for maximum API page size

In 41790caf59ad ("REST: Limit max page size") we limited the maximum page
size to the default page size in the settings.

This turns out to be rather restrictive, as we usually want to keep the
default page size low, but an administrator may want to allow API clients
to fetch more than that per request.

Add a new setting, MAX_REST_RESULTS_PER_PAGE, to set the maximum page size.

Closes: #202 ("Separate max API page size and default API page size into different settings")
Suggested-by: Stewart Smith <stewart@linux.ibm.com>
Suggested-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com>
[dja: set to 250 as per mailing list discussion]
Signed-off-by: Daniel Axtens <dja@axtens.net>