Upgrade test action for NATS Backend

[grischperl]

Description

To ensure full test coverage of the EventingManager, the upgrade flow with NATS Backend needs to be tested.

Job Flow

• Install k3d cluster
• Install NATS (latest release) and wait for readiness
• Deploy eventing-manager (latest release)
• Create Eventing CR with NATS
• Run end-to-end tests (make e2e-eventing-setup and make e2e-eventing)
• Update eventing-manager to input version
• Run end-to-end tests (make e2e-eventing)
• Clean up (make e2e-eventing and make e2e-cleanup)

Useful Links

• GithubAction E2E test with NATS backend exists here
• Installation of NATS is here
• Reusable action is done in BTP Manager here and is called here to be executed on PRs

Acceptance

• GithubAction executes upgrade test with NATS backend on PRs on main and release-* branches
• Action is reusable in other actions, f.ex the release flow