* Add Fastly SSL validation fields
The ssl_hostname field has been deprecated by Fastly. Instead the new
standard is to use the ssl_cert_hostname and ssl_sni_hostname fields:
- ssl_cert_hostname: Used only for certificate verification.
- ssl_sni_hostname: Used only for SNI in the handshake.
Add these fields to the backend block to better support SSL services.
* Add deprecation notice for ssl_hostname