Add profiling_testing namespace to deviceconfig allowlist

This namespace is used only for debug commands intended to be accessible to app developers for the purpose of testing profiling functionality. Profiling has another namespace, "profiling", which is used for actual configs.

Current configs in this namespace include:
- Disable the Profiling rate limiter
- Retain all Profiling results in temporary directory for debugging access.
- Force start a system triggered background trace

Bug: 378176117
Change-Id: I3670bfd71fbaca3509f652402590b9804bcb05a0
Test: presubmit
Flag: EXEMPT - n/a