Better error message when connecting to Capella without TLS

Suggested release note:

If you try to connect to Capella without enabling TLS, now you'll get an exception that says TLS is required (instead of an UnknownHostException, which was downright confusing).

When connecting to Capella without TLS, the SDK reports UnknownHostException, which is misleading.

To reproduce the issue, use the address of a Capella cluster without enabling TLS. Instead of a helpful error message, you'll see something like:

[com.couchbase.endpoint][EndpointConnectionFailedEvent][1024us] Connect attempt 4 failed because of UnknownHostException: example.cloud.couchbase.com {"circuitBreaker":"DISABLED","coreId":"0xf3f7b83e00000001","remote":"example.cloud.couchbase.com:8091","type":"MANAGER"}