RESTEASY-1815 Prepare tests for SSE integration

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• Resolved

RESTEASY-1819 SseBroadcaster.onClose() is not called when SseEventSink is closed or after client connection is closed.

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• Resolved

RESTEASY-1816 OnComplete callback registered via SseEventSource.register() is not called

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• Resolved

RESTEASY-1742 SSE - filters are not picked up, works for normal endpoints

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• Closed

RESTEASY-1733 Sse can't server for a get url without "Accept: text/event-stream" header

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• Closed