lnrpc+lncli: adds required reserve rpc & cli

lnrpc/walletrpc/walletkit.proto

@@ -64,6 +64,14 @@ service WalletKit {
     */
     rpc ListAccounts (ListAccountsRequest) returns (ListAccountsResponse);
 
+    /*
+    RequiredReserve returns the minimum amount of satoshis that should be kept
+    in the wallet in order to fee bump anchor channels if necessary. The value
+    scales with the number of public anchor channels but is capped at a maximum.
+    */
+    rpc RequiredReserve (RequiredReserveRequest)
+        returns (RequiredReserveResponse);
+
     /*
     ImportAccount imports an account backed by an account extended public key.
     The master key fingerprint denotes the fingerprint of the root key
@@ -400,6 +408,16 @@ message ListAccountsResponse {
     repeated Account accounts = 1;
 }
 
+message RequiredReserveRequest {
+    // The number of additional channels the user would like to open.
+    uint32 additional_public_channels = 1;
+}
+
+message RequiredReserveResponse {
+    // The amount of reserve required.
+    int64 required_reserve = 1;
+}
+
 message ImportAccountRequest {
     // A name to identify the account with.
     string name = 1;