Support multiple peer files from environment variable

[ceresnam]

This change enables specifying multiple WireGuard configuration files for the extract_names_config_files option using the PROMETHEUS_WIREGUARD_EXPORTER_CONFIG_FILE_NAMES environment variable.

It utilizes std::env::split_paths to automatically handle the correct OS-specific path list separator (: for Linux/Unix, ; for Windows).

Example (Environment Variable):

PROMETHEUS_WIREGUARD_EXPORTER_CONFIG_FILE_NAMES="/tmp/wg1/conf:/tmp/wg2.conf" prometheus_wireguard_exporter

This correctly parses as:

[INFO] using options: Options { extract_names_config_files: Some(["/tmp/wg1/conf", "/tmp/wg2.conf"]) }

This complements the existing command-line functionality:

prometheus_wireguard_exporter -n /tmp/wg1/conf /tmp/wg2.conf

Which also parses as:

[INFO] using options: Options { extract_names_config_files: Some(["/tmp/wg1/conf", "/tmp/wg2.conf"]) }

[PascalKu]

Nice improvement, thank you! Using std::env::split_paths is a good choice since it automatically handles platform-specific separators.

One thought from my side: the current implementation applies split_paths to all values, including those coming from the CLI. CLI arguments are already provided as separate values by clap, so this may unintentionally split paths that legitimately contain the separator character.

[PascalKu]

This splits all inputs, including CLI arguments already parsed by clap. A CLI path containing : or ; could be incorrectly split. split_paths should only be applied when parsing the environment variable, not CLI-provided values.