I'm not one who tends to ask questions - normally I just Google everything and I can find an answer. But, I can't seem to find an answer this time round. 
The question is:
Based on the Assignee of a Support Request (ticket), I would like to be able to automatically add Watchers depending on the Assignee? For example:
If the Assign is John Smith the watchers should be:
Is this possible. If so how can I do this?
About our Service Desk:
I am currently using the latest version of Jira Service Desk Cloud. And I would like to use it native features if possible. I would prefer not to use any plugins, but if plugins are needed it will need be something that I will have to look into.
Your help will be greatly appreciated.