chore: Enable TLS connection to postgres on newer OTP versions

[nwittstruck]

Description

The upgrade to otp 25 causes issues in postgrex, see elixir-ecto/postgrex#602 and elixir-ecto/postgrex#463. Besides setting ssl: true, we also need to configure the ssl opts properly, i.e. set verify_peer, indicate the server name and and implement a hostname check.

   ssl: System.get_env("DATABASE_SSL", "true") == "true",
   ssl_opts: [verify: :verify_peer,
               cacerts: :public_key.cacerts_get(), # supported with OTP26
               versions: [:"tlsv1.3"],
               depth: 3,
               server_name_indication: String.to_charlist(System.get_env("DATABASE_HOST")),
               customize_hostname_check: [
                match_fun: :public_key.pkix_verify_hostname_match_fun(:https)
               ]
              ]

How SSL/TLS work in elixir in general:
https://erlef.github.io/security-wg/secure_coding_and_deployment_hardening/ssl

Checklist

• Make sure that non-ssl still works for local development
• Test connection in production
• Upgrade elixir, otp and postgrex