Detect internal redirection

**Is your feature request related to a problem? Please describe.**
Detect internal redirect, ex: / -> /index.html

**Describe the solution you'd like**
Expose `r->internal` see: https://github.com/nginxinc/nginx-otel/blob/main/src/http_module.cpp#L312

**Describe alternatives you've considered**
No alternative founded

**Additional context**
No more context