feat: return organisationId if user is an organization

this will help to determine if an event is created by the user or not

WebApp/Endpoints/GeneralUseHelperFunctions.cs

@@ -54,6 +54,12 @@ public class GeneralUseHelpers
         return org;
     }
 
+    async public Task<Organisation?> GetOrganisationFromUserId(int userId)
+    {
+        Organisation? org = await _context.Organisations.FirstOrDefaultAsync(o => o.UserId == userId);
+        return org;
+    }
+
     public string? GetTokenStrFromHTTPContext(HttpContext httpContext)
     {
         var cookies = httpContext.Request.Cookies;