Improve CI/CD for the repo. about darknode-cli

[loongy]

Are these tests going to be run by GitHub Actions, or are they expected to be run by the user on-demand? We should specify that the VPS accounts we use for this must be separated from the main VPS accounts we use so that compromising the CI will not compromise the main accounts.

[loongy]

This issue should probably describe the exact commands we will be testing, in what order. For example: we will do darknode up, then darknode version, then darknode down (obviously we want a few different workflows, many of which will be a bit more complex than this).

[loongy]

@tok-kkk let's proceed with GitHub Actions, just because it allows us to keep as much as possible on GitHub, and we can cut down on an external service. GitHub Actions also seems to be a little more reliable recently. RE: the testing ssh command, we can omit that from testing in these tests.

[loongy]

CI should be triggered on every new commit.

This might be a bit extreme, since these tests are probably going to take a decent amount of time to actually execute in full. I would recommend that we only run them on attempts to merge into master (eg. PRs into master).