api: event stream should allow topic without filter

[tgross]

When using the Go API to read from the event stream, the API documentation says the topic filter is optional. But if omitted, we end up not sending any topic parameter. Making an event stream query without a topic or with a * wildcard topic filter is only allowed by the management token.

If the developer provides a topic without a filter, treat this as a bare topic request as one would expect.

Fixes: #27063

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Changes to Security Controls

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[gulducat]

LGTM!