config: Make the pipe_size field optional

Add the serde default attribute to the field so that parsing
can continue if this field is not present.
The agent assumes a default value for this, so it is not required
by the user to provide a value here.

Signed-off-by: Archana Shinde <archana.m.shinde@intel.com>

src/libs/kata-types/src/config/agent.rs

@@ -80,6 +80,7 @@ pub struct Agent {
     pub kernel_modules: Vec<String>,
 
     /// container pipe size
+    #[serde(default)]
     pub container_pipe_size: u32,
 }