docs: add guide on how to run nwaku from a droplet

[jm-clius]

Background

This issue relates to #828 and forms part of #1003.

Although the operator guide goes some way to explain to operators how to set up and dimension their own nwaku nodes, we still lack step-by-step tutorials for specific run/computing environments. A community member unfamiliar with cloud computing platforms, for example, may want to know how they can configure a long-term running nwaku instance without having access to their own hardware. Someone else may want to get instructions for running nwaku on a Raspberry Pi. Note that the idea is not to promote a specific set of hardware or a specific cloud computing provider, but simply to make the operator guide as accessible as possible with example configurations.

Since many developers already use Digital Ocean droplets, a good first step would be to add a how-to guide for getting nwaku to run a droplet.

Acceptance criteria

Simple how-to guide with:

• quickstart on how to spin up a droplet of sufficient size (no need to repeat Digital Ocean tutorials here - could just mention most obvious steps and link to DO docs for more advanced configuration)
• script to copy nwaku binary to Droplet
• script to run nwaku on this Droplet with at least default configuration (relay + store) + domain name configured + DNS discovery enabled (could link to other how-to page) + discv5 enabled
• how to verify that it is indeed running

Monitoring instructions, more advanced deployment configuration, Grafana dashboards etc. can be included in a subsequent PR.

Research track

This forms part of the operator-outreach track.