Document reporter IPC environment settings

[tahigash]

Summary

• Document PYATS_REPORTER_TIMEOUT and PYATS_REPORTER_MAX_RETRIES in the Reporter overview.
• Include defaults, positive-integer requirements, fallback behavior, and scope of the settings.
• Add a short pyats run job example showing both variables.

Validation

• git diff --check
• DEVNET=false make docs using a temporary Python 3.12 environment and local pyATS source packages; completed successfully with existing Sphinx warnings.