Suggest Doc updates for Android network-security interaction

In this forum post:
https://forums.couchbase.com/t/server-tls-certificate-untrusted-error-connecting-to-sync-gateway/29087/7

Jeff Lockhart implies that the interaction between replicators and Android's network-security configuration is more complex than we suspected. In particular:

apparently there’s a requirement that if you have a <domain-config> defined (“Domain specific configuration”), even if it’s to set cleartextTrafficPermitted="true", it requires implementing checkServerTrusted(X509Certificate[], String, String) in some way. This function is part of the X509TrustManager API.

We need to do a couple of experiments to understand the interaction, and then describe it in the Android documentation