Adjust timeout when validateEmail configured

[davidmytton]

A user has reported seeing some timeouts when using the validateEmail rule. In some cases, this can take several hundred ms to return when it performs the MX record lookup. In those cases, we're limited by the network call to the domain and the speed of the DNS response.

A slower response here should still be under the prod timeout of 500ms when making a call to our API in the same region, but this user was seeing it when testing locally. In their case, the API was some 100ms of network latency distance. Combined with the slower API response, this was triggering timeouts.

If there is an email check being performed, we should consider setting the timeout to a higher value. We aim for a very fast response because some rules are likely to be high volume e.g. rate limiting or bot detection. However, we can probably relax that slightly for email validation, which should be much lower volume. The rate limit and bot detection rules always run first, so if they return a deny decision then the email rule won't run.