Support merging object templates for REST API

[chuan137]

Is your feature request related to a problem? Please describe.
extend default REST API object templates

Describe the solution you'd like
Currently, I can only extend the REST objects by overriding. I would like to extend by merging like ZAPI, i.e., use a custom template and harvest will merge it with the default configuration.

Describe alternatives you've considered
...

Additional context
discussion on discord: https://discord.com/channels/855068651522490400/1200761327191343214/1201388551141601310

[cgrinds]

Thanks for the feature request @chuan137 we'll take a look