vmq_diversity: dd useful SSL Client opts for Postgres

[ioolkos]

Just as a quick example, in relation to #2282

Example config: (in addition to plugin/host/port configs)

vmq_diversity.postgres.ssl = on
vmq_diversity.postgres.ssl.verify = verify_peer
vmq_diversity.postgres.ssl.customize_hostname_check = https
vmq_diversity.postgres.ssl.depth = 10
vmq_diversity.postgres.ssl.use_system_cas = on

use_system_cas loads the system CA's; alternatively you can configure a cafile with:

vmq_diversity.postgres.ssl.cafile = path/to/ca.pem

vmq_diversity.postgres.ssl.customize_hostname_check = https switches hostname checks to https style, allowing for wildcard certs.