Serialize the RenderBlogPost to JSON.

This struct still does not contain anything, but I'm just setting up the skeleton for this code.

src/error/error.rs

@@ -6,6 +6,7 @@ pub(crate) enum CustomError {
     TomlDeserialize(toml::de::Error),
     WalkDir(walkdir::Error),
     Tokio(tokio::task::JoinError),
+    Serde(serde_json::Error),
 }
 
 impl From<std::io::Error> for CustomError {
@@ -43,3 +44,9 @@ impl From<tokio::task::JoinError> for CustomError {
         CustomError::Tokio(value)
     }
 }
+
+impl From<serde_json::Error> for CustomError {
+    fn from(value: serde_json::Error) -> Self {
+        CustomError::Serde(value)
+    }
+}