Improve logging in the Rust part

[imobachgs]

• agama-web-server writes now to the stdout if it is not connected to journald.
• agama-dbus-server uses tracing.
• The stdout logger now includes the file/line. They were already included in the journal logs.

2024-05-15T15:30:42.816878Z  WARN agama_server::network::nm::client: agama-server/src/network/nm/client.rs:155: Ignoring network device on path /org/freedesktop/NetworkManager/Devices/1
2024-05-15T15:30:42.845629Z  INFO agama_server::web::service: agama-server/src/web/service.rs:91: Serving static files from /usr/share/agama/web_ui
2024-05-15T15:30:42.901972Z  INFO agama_web_server: agama-server/src/agama-web-server.rs:253: Starting Agama web server at 0.0.0.0:443
2024-05-15T15:30:42.901993Z  INFO agama_web_server: agama-server/src/agama-web-server.rs:253: Starting Agama web server at 0.0.0.0:80

[jreidinger]

should we return here error if logging failed to be initialized?

[imobachgs]

It should return an error (see the ? sign).

[coveralls]

coverage: 69.889%. remained the same
when pulling c521683 on logging
into 3ef5965 on master.