feat: add logic that lets users favorite a template

[nickoferrall]

Fix #9115

Loom demo: https://www.loom.com/share/d59162967e244522aa40b73290a9c9a8

AC

• Can favourite a template and see it show up in your favourites section
• Can un-favourite a template
• Can favourite and unfavourite a template from the template details view

[Dschoordsch]

The heart seems a bit misaligned for me (Safari, Mac), slightly too high on the card and more so on the category. It also conflicts with the "custom" badge on master, but we could remove that one again.

[Dschoordsch]

+1 Seems excessive to return the full user. I think it would be enough to return the updated template and favourite state.

[nickoferrall]

I've moved the heart in the card to be slightly lower and to the right. For the custom label, we have a separate discussion in Slack around that.

In the category labels, I think it is centred:

[Dschoordsch]

I don't want to be picky, but the category heart is offset 2px to the top

We also need to do something about the custom label first before merging.

[nickoferrall]

For the custom label, once you and Terry have reached a decision in the Slack discussion, I can update this PR or wait for the "Custom" label to be reverted/changed.

I don't want to be picky, but the category heart is offset 2px to the top

On Chrome, it was centered for me, but I can see the 2px offset on Safari. I've pushed an update and now it's centered on Safari for me, too: