Channel vs Context Field When Creating WebSocket API

[hisanhunais]

Description:
In [1], under Step 3, there is a description regarding a field called Context in the table, but in the UI, the field is Channel. Hence, better to make Context as Channel with a proper description.

The change should be made to 4.x.x doc versions

[1] https://apim.docs.wso2.com/en/latest/design/create-api/create-streaming-api/create-a-websocket-streaming-api/#step-1-design-a-websocket-api