Refactoring tests to remove the Vert.x usage and dependencies

[ppatierno]

With the bridge core reducing the Vert.x usage at the minimum, we should aim to do the same with tests.

• The Vert.x Kafka client could be replaced by the "official" Kafka Java client (provided by the upstream Kafka community)
• The Vert.x Web client could be replaced by the plain Java HTTP client (provided by the SDK itself)
• The Vert.x OpenTracing won't be needed anymore because we are going to remove OpenTracing support as planned
• The Vert.x OpenTelemetry could be replaced by the "official" OpenTelemetry instrumentation library
• The Vert.x Junit 5 maybe replaced by just Junit (?)