[feature] Rego debugger

[anakrish]

According to Open Policy Agent/ecosystem/debugging_rego "Debugging Rego policies can be tricky". There is no way to step through the evaluation of a rego policy.

We need to implement a debugger for Rego policies. Since Rego does not have mutable variables, the debugger implementation ought to be much simpler than for a language with mutable variables.

Idea/Early implementation here: main...anakrish:regorus:debugger