ci: e2e test suite

[mudler]

It would be good practice to have CI tests that are gating PRs, and also to guarantee the state of the project main branch.

This card is about creating the e2e test suite for the project, which will be run by the Github action runner to gate changes.

The e2e tests should leverage the features of the oracle from an user-perspective, and run tests for each of the functionalities.

This ticket is to have a small initial e2e test suite leveraging the basic aspects of the node ( startup and answering to API requests).

Acceptance criteria

• we have a github workflow that runs on PR, main branch and releases which exercise the code. The test suite is named "e2e test"
• the e2e test will exercise for now very basic checks, for instance configuration of the node, starting the oracle node and the API server and see if basic routes (e.g. the swagger API) runs correctly.