ci: prepare testnet-1 env

[sebastiendan]

Description

This PR adds a docker build workflow run for the testnet-1 environment.

PR Checklist:

• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added or updated tests that comprehensively prove my change is effective or that my feature works