Add new env variables for new doh config keys

[satishweb]

Ref: m13253/dns-over-https#167 (comment)

Add new variables for below doh server config keys:

log_guessed_client_ip
ecs_allow_non_global_ip
ecs_use_precise_ip
tls_client_auth
tls_client_auth_ca
local_addr
cert
key