Add OIDC e2e test mt-broker

[creydr]

We should add e2e tests, which test the flows through the mt-broker:

Simple flow:

Simply check, that a event goes through the broker to the sink.

flowchart LR
    SOURCE[Source] --> BROKER[Broker with Audience]
    BROKER --> TRIGGER[Trigger]
    TRIGGER --> SINK[Sink with Audience]

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With Reply:

Check that a reply from the sink is received well by the Broker (which has an audience).

flowchart LR
    SOURCE[Source] -->|eventtype-1| BROKER[Broker with Audience]
    BROKER --> TRIGGER[Trigger with filter for eventtype-1]
    TRIGGER --> SINK[Sink with Audience]
    SINK -->|respond with eventtype-2| TRIGGER
    BROKER --> TRIGGER2[Trigger with filter for eventtype-2] --> SINK2[Sink 2]

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The 2nd Trigger (with filter for eventtype-2) is only to ensure, that the broker received a reply and thus the sink 2 does not need an Audience configured.

With Dead Letter Sink:

Check that a dead letter sink request gets delivered correctly, if the DLS has an Audience.

flowchart LR
    SOURCE[Source] --> BROKER[Broker with Audience]
    BROKER --> TRIGGER[Trigger with Dead-Letter-Sink]
    TRIGGER --> SINK[Sink with Audience]
    SINK -->|respond with non retryable Statuscode| TRIGGER
    TRIGGER --> DLS[Dead-Letter-Sink with Audience]

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Requires the following issues to be done:

• Update channel dispatcher to authenticate requests #7364
• mt-broker-ingress: reject request for wrong audience #7290
• mt-broker-filter: reject request for wrong audience #7291

[creydr]

Done in #7480