tools: add logfmt option for frr-reload.py

tools: add logfmt option for frr-reload.py

Add the option of printing logs in logfmt format.

Additional machine readable information can be printed via the `extra`
argument.
Example:
```python
log.debug("exit context"), extra={"line": line, "ctx_keys": ctx_keys})

log.error(f"Failed to execute command {' '.join(cmd)}", extra={"cmd": cmd})
```

Signed-off-by: Giovanni Tataranni <g.tataranni@gmail.com>