Add animations codelab to codelabs.yml

[johnpryan]

No description provided.

[flutter-website-bot]

Visit the preview URL for this PR (updated for commit 037c268):

https://flutter-docs-prod--pr11906-add-animations-codelab-3qiu8v4o.web.app

[sfshaza2]

I'm confused. When I look at the staged version of this PR... on the "Tutorials and samples" page, I can filter by "animations" and there it is!! But when I filter by "How to" (and only "How to"), it's NOT there. (I scrolled through several times to make sure I didn't miss it.)

[johnpryan]

Interesting, I don't see any of our codelabs showing up when I filter for "how-to", but I think they probably should. @ericwindmill WDYT?

[ericwindmill]

@sfshaza2 @johnpryan -- I think you're right.

In fact, I'm not sure that the "type" of 'how to' makes sense. I was attempting to make a more generalized category for cookbook recipes. I'm not sure why I tried to get clever. I'll make a follow up PR to make the terminology clearer.