allow passing of configuration

Author: cbaker6

Sources/ParseServerSwift/configure.swift

@@ -4,10 +4,15 @@ import Vapor
  A helper method for configuring your `ParseServerSwift`. This should only be called once when starting your
  Vapor app.
  - parameter app: Core type representing a Vapor application.
+ - parameter configuration: A `ParseServerConfiguration`. If `nil`, the vapor
+ environment variables will be used for configuration.
  */
-public func parseServerSwiftConfigure(_ app: Application) async throws {
+public func parseServerSwiftConfigure(
+    _ app: Application,
+    configuration: ParseServerConfiguration? = nil
+) async throws {
     // Initialize ParseServerSwift
-    let configuration = try ParseServerConfiguration(app: app)
+    let configuration = try configuration ?? ParseServerConfiguration(app: app)
     try await ParseServerSwift.initialize(configuration, app: app)
 
     // register routes