Propose support for custom CA cert

Signed-off-by: Joe Nathan Abellard <contact@jabellard.com>

docs/proposals/karmada-operator/custom_ca_cert/README.md

@@ -26,7 +26,7 @@ and disaster recovery is essential. Deploying control planes across multiple man
 However, when multiple control plane instances must access a shared etcd instance and present a unified API endpoint, using a common CA certificate across instances is necessary. 
 By enabling users to specify a custom CA certificate, this feature ensures that control planes spanning data centers function as a cohesive unit while meeting security and availability standards.
 
-### Architecture Overview:
+### Architecture Overview
 ![architecture-overview](./architecture-overview.png)
 
 ### Goals