Export app-crypto specific keystore functions (#7489)

* Export app-crypto specific keystore functions

* Also add back the insert function

* Switch KeystoreContainer to an enum

* Only export the bare minimal for LocalKeystore and fix service compile

* fix: should return Arc

* Add docs stating that functions only available in local keystore

* Remove insert and generate functions

* fix: generate function should be available in test

* Add keypair function to trait

* Revert "Add keypair function to trait"

This reverts commit ad921b09ca73d3c09298e3a51b562ef8e0067781.

* Add note for local_keystore function in service

substrate/client/service/src/builder.rs

@@ -205,12 +205,13 @@ pub type TLightClientWithBackend<TBl, TRtApi, TExecDisp, TBackend> = Client<
 	TRtApi,
 >;
 
-/// Construct and hold different layers of Keystore wrappers
-pub struct KeystoreContainer {
-	keystore: Arc<dyn CryptoStore>,
-	sync_keystore: SyncCryptoStorePtr,
+enum KeystoreContainerInner {
+	Local(Arc<LocalKeystore>)
 }
 
+/// Construct and hold different layers of Keystore wrappers
+pub struct KeystoreContainer(KeystoreContainerInner);
+
 impl KeystoreContainer {
 	/// Construct KeystoreContainer
 	pub fn new(config: &KeystoreConfig) -> Result<Self, Error> {
@@ -221,22 +222,36 @@ impl KeystoreContainer {
 			)?,
 			KeystoreConfig::InMemory => LocalKeystore::in_memory(),
 		});
-		let sync_keystore = keystore.clone() as SyncCryptoStorePtr;
 
-		Ok(Self {
-			keystore,
-			sync_keystore,
-		})
+		Ok(Self(KeystoreContainerInner::Local(keystore)))
 	}
 
 	/// Returns an adapter to the asynchronous keystore that implements `CryptoStore`
 	pub fn keystore(&self) -> Arc<dyn CryptoStore> {
-		self.keystore.clone()
+		match self.0 {
+			KeystoreContainerInner::Local(ref keystore) => keystore.clone(),
+		}
 	}
 
 	/// Returns the synchrnous keystore wrapper
 	pub fn sync_keystore(&self) -> SyncCryptoStorePtr {
-		self.sync_keystore.clone()
+		match self.0 {
+			KeystoreContainerInner::Local(ref keystore) => keystore.clone() as SyncCryptoStorePtr,
+		}
+	}
+
+	/// Returns the local keystore if available
+	///
+	/// The function will return None if the available keystore is not a local keystore.
+	///
+	/// # Note
+	///
+	/// Using the [`LocalKeystore`] will result in loosing the ability to use any other keystore implementation, like
+	/// a remote keystore for example. Only use this if you a certain that you require it!
+	pub fn local_keystore(&self) -> Option<Arc<LocalKeystore>> {
+		match self.0 {
+			KeystoreContainerInner::Local(ref keystore) => Some(keystore.clone()),
+		}
 	}
 }