Tezt_cloud: Unify snapshot mechanism between LAYER1 and DAL scenarios

What

In this MR we achieve the following:

• we unify the --network CLI option between the DAL and LAYER1 scenarios
• we unify the --snapshot CLI option between the DAL and LAYER1 scenarios
• we deduplicate and refactor the snapshot verification and import logic between the two scenarios

Why

So that the scenarios follow a similar procedure as much as possible. This approach is more scalable (for more projects/features per project), so that we do not re-invent the wheel every time.

How

Manually testing the MR

This is not trivial/precise. Basically, what I tried so far is to check that the DAL and LAYER1 scenarios have not changed their behaviours.

Additionally, now we can have a URL argument for the --snapshot argument in the DAL scenario. Tested and it looked fine with:

dune exec tezt/tests/cloud/main.exe -- DAL --producers 2 --network ghostnet --tezt-cloud dal_with_snapshot --keep-temp -v --snapshot "https://snapshots.tzinit.org/ghostnet" --localhost --fundraiser edsk3nd3m5Zb31fbchqAvWVUbeF4jH7kdcs6mRCA7rFzYt4kopSyZP

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR