MINOR: http_fetch: Add case-insensitive argument for url_param/urlp_val

MINOR: http_fetch: Add case-insensitive argument for url_param/urlp_val

This commit adds a new optional argument to smp_fetch_url_param
and smp_fetch_url_param_val that makes the parameter key comparison
case-insensitive.
Now users can retrieve URL parameters regardless of their case,
allowing to match parameters in case insensitive application.
Doc was updated.