Welcome Tour: Explore new design for Header controls

### What

[Introducing new gifs ](https://github.com/Automattic/wp-calypso/pull/56347) for the mobile Welcome Tour, we encountered some problems with the tour overlay controls overlapping with the gifs.

We shipped a [quick solution](https://github.com/Automattic/wp-calypso/pull/59052), but that's not optimal.

We talked about this in the pod slack thread: p1639497273123400-slack-C029WSAQMT9

### How

I'll try to cover in bullet points the conversation we had on Slack and what we should do:

- Header controls overlap with imgs/gifs. Possible solutions:
-- Background image with negative margin
-- ...
- Header controls may be too big, grabbing a bit too much attention.
- Hover effect on desktop (non-touch enabled devices):
-- Might be an accessibility issue
-- Not optimal CSS solution used for that ([56164](https://github.com/Automattic/wp-calypso/pull/56164))
-- Always showing the controls seems like a more modern solution