rds_json_user_property can not set int value

[xiaohuilam]

rds_json_user_property can not set int value to a property,
if will translation int value into a string.

[agentzh]

@xiaohuilam Because literal values specified directly in nginx.conf are all strings per se. That is, 32 is exactly equivalent to "32" to the nginx config file parser. We could add a third (optional) argument to the rds_json_user_property directive so as to specify a different value type, for example,

rds_json_user_property age 26 int;

Patches welcome :)