[sr-dev] [kamailio/kamailio] make ruxc build optional (#2808)

### Description

I during master compilation I see an error ``` [root@safarov-dell kamailio]# make -C src/modules/ruxc/ make: Entering directory '/tmp/kamailio/src/modules/ruxc' CC (gcc) [M ruxc.so] ruxc_mod.o ruxc_mod.c:28:10: fatal error: ruxc.h: No such file or directory 28 | #include <ruxc.h> | ^~~~~~~~ compilation terminated. ``` I was not able to figure out how to install the required dependency on CentOS dist and Fedora. Could you make build this module build optional