App: Add a final "Change skin" option rather than changing per skin click.

[keston-dev]

Please confirm the following.

• I checked the existing issues for duplicate feature requests
• I have checked that this feature request is not on our roadmap

What parts of Modrinth is your feature request related too?

Modrinth App

Is your suggested feature related to a problem? Please describe.

With the current implementation of the (beta) skin feature, changing skins immediately sends the requests to Mojang, resulting in a 429 if you click too quickly.

Describe the solution you'd like

Id prefer a final "Change skin" button, which allows you to use the left-side preview without having to actually change your skin.

Describe alternatives you've considered

No response

Additional context

No response