The `ELBSecurityPolicy-FS-1-2-Res-2020-10` policy is the most
restrictive TLS v1.2 only SSL/TLS security policy available, and is a
subset of the already accepted `ELBSecurityPolicy-FS-1-2-Res-2019-08`
policy - this commit adds `ELBSecurityPolicy-FS-1-2-Res-2020-10` to
the list of acceptable "secure" security policies.
`ELBSecurityPolicy-FS-1-2-Res-2020-10` has a very limited set of
ciphers, is TLS v1.2 only and supports Forward Secrecy.
Current SSL Labs tests gives it an "A" rating for another source of
confirmation.