Make LOG_FORMAT work for access logs, allow custom access log format

[khvn26]

Is your feature request related to a problem? Please describe.

Currently, access log format is hardcoded.

This prevents users from customising their access log output.

Additionally, setting LOG_FORMAT does not apply the JSON formatting to the access logs.

Describe the solution you'd like.

Implement the following:

1. Support setting custom logconfigs — either logconfig, logconfig_dict or logconfig_json command line options.
2. Set up a log formatter (e.g. this JSON formatter) depending on how LOG_FORMAT is set.

Describe alternatives you've considered

N/A

Additional context

No response