Implemented simple, structured data logging

[forman]

xcube server can now be configured to produce structured data logs. If data_logging is true server requests are logged in form of JSON data records, that can be machine-detected and -parsed by lines starting with a { character.

Currently only applies to logging of HTTP requests.

Closes #1060.

Sample log entry:

{"timestamp": "2024-08-16 07:50:58.028860", "level": "INFO", "status": 200, "user_id": null, "duration": 102, "request": {"method": "GET", "uri": "/tiles/local/conc_tsm/8/83/128?crs=EPSG%3A3857&vmin=0.0672554675129238&vmax=30&cmap=cc_tsm&time=2017-01-16T10%3A09%3A21Z", "host": "localhost:8080", "protocol": "http", "remote_ip": "127.0.0.1", "user_agent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/127.0.0.0 Safari/537.36 Edg/127.0.0.0"}}

Checklist:

• Add unit tests and/or doctests in docstrings
• Add docstrings and API docs for any new/modified user-facing classes and functions
• New/modified features documented in docs/source/*
• Changes documented in CHANGES.md
• GitHub CI passes
• AppVeyor CI passes
• Test coverage remains or increases (target 100%)