Tezt: Make the [Dac_node] module compatible with [Client.endpoint]

Context

Follow the approach used by the Client module to not assume it communicates with an Octez node managed by Tezt. This generalizes the Dac_node module.

This is useful in the context of using Tezt as a scenario orchestrator, and makes it possible to run the dac node against a public endpoint like the one kindly provided by Oxheadalpha for Mondaynet for instance.

Manually testing the MR

The CI should give you enough insight, hopefully. The changes are supposed to be fully backward compatible.

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