feat(api): implement endpoint for creating link tokens

src/FiscalOS.API/Institutions/Link/Response.cs

@@ -0,0 +1,19 @@
+namespace FiscalOS.API.Institutions.Link;
+
+public sealed record Response
+{
+  public string LinkToken { get; init; } = string.Empty;
+
+  [JsonConstructor]
+  private Response()
+  {
+  }
+
+  public static Response From(string linkToken)
+  {
+    return new()
+    {
+      LinkToken = linkToken,
+    };
+  }
+}