Adds JWT secret, turns on Swagger UI, and cleans up refresh token response

src/main/kotlin/net/halfbinary/scavengerhuntapi/model/converter/RefreshConverter.kt

@@ -0,0 +1,7 @@
+package net.halfbinary.scavengerhuntapi.model.converter
+
+import net.halfbinary.scavengerhuntapi.model.response.RefreshResponse
+
+fun String.toRefreshResponse(): RefreshResponse {
+    return RefreshResponse(this)
+}

src/main/kotlin/net/halfbinary/scavengerhuntapi/model/response/RefreshResponse.kt

@@ -0,0 +1,5 @@
+package net.halfbinary.scavengerhuntapi.model.response
+
+data class RefreshResponse(
+    val accessToken: String
+)