Change log for ZSCALER_WEBPROXY

Date Changes
2022-06-20 Enhancement - Mapped 'metadata.product_name' to 'Zscaler Web Proxy' for logs that do not contain the field 'product'.
Added conditional check for the field 'url' mapped to UDM field 'target.port'.
2022-05-31 Enhancement-Added grok pattern for failing SIEM logs in csv format that were
dropped with error.