CTL - add variadic arguments API

# Add variadic arguments API
This issue introduces generic CTL API for the following functions:
```cpp
umfCtlGet(const char* name, ...);
umfCtlSet(const char* name, ...);
umfCtlexec(const char* name, ...);
```
Current API contains explicit arguments like:
```cpp
int umfCtlGet(const char *name, void *ctx, void *arg);
```