We never tried to configure the SAP Host Agent auto upgrade but looking at the steps, seems like a bit straight forward. If you want to enable this feature, you might follow below guides which provided by SAP.
Copied from SAP Help website,
SAP Host Agent is enabled to check for updates automatically and get upgraded if a version of the SAP Host Agent executable is found that is higher than the existing one.
• Automated Upgrade of SAP Host Agent
• Configuring the Automated Upgrade Behavior of SAP Host Agent
• Avoiding Incomplete Upgrade of SAP Host Agent
• Configuring Delayed Auto-Upgrade of SAP Host Agent to Avoid Network Bottlenecks
• SAP Note 1473974 (Refer to the attachment).
