[CLOUDS-8163] Support Debug Logging For the Result of All Azure CLI Commands.

[perzycharles]

add --log-level debug support for azure CLI command logging

• Log stdout of each azure CLI command at DEBUG level in execute_cmd.py
• Add --log-level arg parsing and basicConfig() to app_registration and log_forwarding quickstart entry points so the flag actually takes effect.

This is motivated by CLOUDS-8163. Without the stdout, it's hard to debug where the script has problem.