Auto-generate and deploy `docker.config` as part of the cronjob

[vpetersson]

The miner is automatically pulling docker.config as part of the start process. However, this file is currently served from helium-assets.nebra.com, which in turn isn't automatically generated and deployed.

I suggest that we:

• Update the GitHub Workflow to use the master branch for 'TestNet' and the production branch for MainNet.
  • This way we can easily test new GA and breaking changes on TestNet without impacting MainNet
• Point all of TestNet to helium-snapshots-stage.nebra.com using the Fleet environment variable OVERRIDE_CONFIG_URL

[shawaj]

@vpetersson it is automatically generated and deployed.... https://github.com/NebraLtd/hm-block-tracker/blob/master/.github/workflows/run-update.yml

[vpetersson]

Ok, need to patch that for staging vs production then.

[vpetersson]

• [x] The docker.config file is now automatically generated as part of the GitHub Actions workflow for stage vs production
• [x] TestNet now points towards the staging environment
• [x] Update the Cronjob to build both staging and production snapshots