Error out on any unknown keys in configs

This will make it very obvious during validate if there are any misspelled
or unmigrated configuration options.

Signed-off-by: Robert Detjens <github@detjens.dev>

Author: detjensrobert

src/configparser/challenge.rs

@@ -118,6 +118,7 @@ pub fn parse_one(path: &PathBuf) -> Result<ChallengeConfig> {
 
 #[serde_nested]
 #[derive(Debug, PartialEq, Serialize, Deserialize)]
+#[serde(deny_unknown_fields)]
 #[fully_pub]
 pub struct ChallengeConfig {
     name: String,

src/configparser/config.rs

@@ -48,6 +48,7 @@ pub fn parse() -> Result<RcdsConfig> {
 //
 
 #[derive(Debug, PartialEq, Serialize, Deserialize)]
+#[serde(deny_unknown_fields)]
 #[fully_pub]
 struct RcdsConfig {
     flag_regex: String,