cloudflared support on cloudflare access DoH address

Hi,
Since cloudflare releases cloudflare access and this is a good thing.

I have problem with local ISP who filter any dns request and forward it to government filtered dns. therefore configuration to use 172.64.36.1 and 172.64.36.2 will be not useful so by then I set it up to use DoH agent cloudflared to calling out cloudflare-gateway

I have current setup with pihole and use cloudflared as DoH agent, with configuration upstream to https://1.1.1.1/dns-query this work great.

but when its changed to https://y6z5ii2u5v.cloudflare-gateway.com/dns-query it cannot perform dns lookup. and when its changed to its ip address instead of domain name which https://162.159.36.5/dns-query\ resulted in tls handshake failure

hopefully, cloudflared will natively support this address.

```
Apr 17 05:13:23 DietPi cloudflared[3414]: time="2020-04-17T05:13:23+01:00" level=error msg="fai
led to connect to an HTTPS backend \"https://162.159.36.5/dns-query\"" error="failed to perform
an HTTPS request: Post https://162.159.36.5/dns-query: remote error: tls: handshake failure"

Apr 17 05:13:28 DietPi cloudflared[3414]: time="2020-04-17T05:13:28+01:00" level=error msg="fai
led to connect to an HTTPS backend \"https://y6z5ii2u5v.cloudflare-gateway.com/dns-query\"" err
or="failed to perform an HTTPS request: Post https://y6z5ii2u5v.cloudflare-gateway.com/dns-quer
y: net/http: request canceled while waiting for connection (Client.Timeout exceeded while await
ing headers)"

```