Rename lifetime to vtxoTreeExpiry (#433)

* rename lifetime to vtxoTreeExpiry

* remove useless init() in config.go

Author: louisinger

api-spec/openapi/swagger/ark/v1/service.swagger.json

@@ -512,7 +512,7 @@
         "pubkey": {
           "type": "string"
         },
-        "roundLifetime": {
+        "vtxoTreeExpiry": {
           "type": "string",
           "format": "int64"
         },

api-spec/protobuf/ark/v1/service.proto

@@ -94,7 +94,7 @@ service ArkService {
 message GetInfoRequest {}
 message GetInfoResponse {
   string pubkey = 1;
-  int64 round_lifetime = 2;
+  int64 vtxo_tree_expiry = 2;
   int64 unilateral_exit_delay = 3;
   int64 round_interval = 4;
   string network = 5;