Problem: Issues using a firewall with our current production node deployment template

## Issues

We have some [docs about firewall setup](https://docs.bigchaindb.com/projects/server/en/v2.0.0a1/appendices/firewall-notes.html) but they are generic and don't apply directly to our [production node deployment template](https://docs.bigchaindb.com/projects/server/en/v2.0.0a1/production-deployment-template/index.html). For example, our production node deployment template uses different port numbers than the ones listed.

Another issue is that when setting up a firewall, one tells it something like "only allow incoming traffic on port N from IP address AA.BB.CC.DD." In principle, that should allow a node to only allow Tendermint traffic from other nodes in the cluster. Unfortunately, the IP address of a node is determined by a Kubernetes Service (the NGINX Service) and it's my understanding that that IP address might change over time.

## Solution

- Move the page about firewall setup into our production node deployment docs, since only production deployments are going to be using a firewall anyway.
- Change the port numbers in those notes about firewall setup to be the same as the ports we actually use in our production deployment template.
- Add some docs to our production node deployment template about how to get a static IP address on Azure. (Something similar is possible on other cloud providers.) Change the YAML file for the NGINX Service to use the static IP address. Update the docs accordingly. Here's some Azure documentation about how to get a static IP address and how to use it in a Kubernetes Service:

https://docs.microsoft.com/en-us/azure/aks/static-ip