Add ApiKeyLocation enum for API key placement options

Introduced the ApiKeyLocation enum in the ReC.Domain.Constants namespace to specify API key locations, supporting both Header and Query options.

src/ReC.Domain/Constants/ApiKeyLocation.cs

@@ -0,0 +1,7 @@
+namespace ReC.Domain.Constants;
+
+public enum ApiKeyLocation
+{
+    Header = 0,
+    Query = 1
+}