getChannelData ({ chanId, channel, symbol, key }) {
    const id = chanId || this._chanIdByIdentifier(channel, symbol || key)

    return this._channelMap[id] || null
  }
Fetch a channel definition

@param {object} opts - options
@param {number} opts.chanId - channel ID
@param {string} opts.channel - channel name
@param {string} [opts.symbol] - match by symbol
@param {string} [opts.key] - match by key (for candle channels)
@returns {object} chanData - null if not found