Button template models are not prefixed with template_

Relates to MC-214689, MC-214690, MC-214691 and probably many others under incorrect-asset-names.

As these models are not used directly, but are instead utilised by a multitude of other model files which apply textures, it'd be expected that these files would be prefixed with "template_", like multiple others are. However, this is not currently the case.

Models in question:

• button.json
• button_inventory.json
• button_pressed.json