Reconsider TLS options for network

[reinkrul]

We now have network.enabletls for disabling TLS on the gRPC network layer, which can only be set when strict mode is disabled. The option is used for local/workshop settings in which TLS is inconvenient.

To make the minimal setup easier for networkless deployments (did:web only), you don't want to configure anything network. related. So:

• Remove network.enabletls configuration flag
• If TLS properties are configured, enable TLS.
• If no TLS properties are configured, disable TLS.
• Require TLS to be configured in strict mode (TLS offloading still works; needs to be explicitly configured)

If we decide to keep the network.enabletls option, we should remove the following log warning:

TLS is disabled, which is only meant for demo/workshop purposes!

[woutslakhorst]

As far as I can see, enabling/disabling based on existence of TLS configuration is fine.