Deprecating .hbs file extension in themes and plugins

[RGJ (Richard - Communiteq)]

Just came across this one, guess it needs to be updated

@david

Templates introduced using this method should be moved to dedicated .hbs files, or refactored into gjs files.

To keep as HBS, connector templates can be placed in:

{theme}/javascripts/discourse/connectors/{outlet-name}/{connector-name}.hbs

and component templates can be placed in:

{theme}/javascripts/discourse/components/{component-name}.hbs