addAgentAttribute(key, value, truncateExempt = false) {
    const shouldKeep = this._checkFilter(key)
    if (shouldKeep) {
      const processedValue = truncateExempt ? value : _truncate(value)
      this._agentAttributes.addAttribute(key, processedValue)
    }
  }
Add a key/value pair to the Span's agent attributes collection.

@param {string} key Name of the attribute to be stored.
@param {string|boolean|number} value Value of the attribute to be stored.
@param {boolean} [truncateExempt] Set to true if attribute should not be truncated.