docs: Add a deployment guide using Test Network

[hajjimo]

One of the Tech Team's goals for 2025 is to improve documentation for integrators. To support that goal, add an end-to-end deployment guide using Test Network as the reference architecture. Beni and Tadej will be the SMEs supporting this task. A separate issue will be created for an end-to-end deployment guide using the Interledger wallet app as an example.