Expose HTTP Endpoints listeners used for metrics

[salaboy]

Right now the /metrics endpoint is automatically created and hosted using port 8080 it will be nice for users to be able to register other HTTP endpoints using the same listener under 8080. Today, looking at the code this is not possible.

[DirectXMan12]

/kind feature
/priority backlog

We usually just serve other things on a different port, but yeah, this could be useful.

[vincepri]

/help

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[hypnoglow]

/assign

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