Function apply_env_at_path 

pub fn apply_env_at_path(
    base: &mut Value,
    env_vars: &[&str],
    path: &[&str],
    decode: EnvDecode,
    overwrite: bool,
) -> Result<(), String>

Reads one key from the environment and writes it into root.

The public entry for callers with a runtime-built key set (the Saluki-only model), which cannot use the 'static EnvKey table. Same semantics as apply_datadog_env for a single key.

Errors

Returns a message when the environment value is malformed for decode.