Make using insecure connections opt-in (#1309)

* add insecure url checks

* rename variables

* add feature flags to expose Url properly

* fix test compile error

* fix feature errors

* remove comment

* add url crate and use it for url parsing

* fix compile errors

* satisfy the holy clippy

* fix typos and host loopback

* macro attribute, provide validation function in utils

* fix expected output of ui tests

* remove the success case for --allow-insecure because we cannot establish ws:// connection at the moment.

subxt/src/error/mod.rs

@@ -115,6 +115,9 @@ pub enum RpcError {
     /// The RPC subscription dropped.
     #[error("RPC error: subscription dropped.")]
     SubscriptionDropped,
+    /// The requested URL is insecure.
+    #[error("RPC error: insecure URL: {0}")]
+    InsecureUrl(String),
 }
 
 impl RpcError {