Change default keyframe type.

[MrSirSquishy]

Detailed description of your suggestion

Currently whenever a keyframe is generated in Blockbench it will default to being a linear keyframe if there's no other influence. Whenever I animate I almost never use linear keyframes aside from niche scenarios, as smooth keyframes are usually much more versatile, hence it would be a good idea to add a way to change what type of keyframe Blockbench defaults to, so that time would be saved if linear keyframes aren't preferred, but people can still default to linear, or even bezier if it is their preference.