Fix ugly installer splash screen

[smallketchup82]

Related: ppy/osu#29773

Turns out that Velopack doesn't support transparent .png's as the splashicon, leading to issues like this on installation:

Velopack supports a:

• High Resolution JPG
• PNG with non-transparent background

This PR reuses https://github.com/ppy/osu/blob/master/osu.iOS/Assets.xcassets/AppIcon.appiconset/300076680-5cbe0121-ed68-414f-9ddc-dd993ac97e62.png for the icon. Though, alternative designs are welcome.

Preview:

You can use this release to test it (you must not have lazer installed first)

Testing Checklist

• Test deploy
• Test installation
  Works as expected for me!

[smallketchup82]

Moved the file into osu-deploy. Not sure if we want it in an assets folder or not, but seeing as install.ico is in the root folder, I decided to place the splash image in the root folder as well. Let me know if you have another location in mind.

I'm still yet to test these changes, so I'll keep this PR as a draft until I do.

[peppy]

Looks blurry to me:

[peppy]

It seems velopack doesn't handle high dpi displays correctly for the splash icon.

[alexoshowo]

idk if i can place ideas out here, like in previous now closed pr, but if i can, i suggest to show some kind of artwork or something

[peppy]

That's what I was hoping for. Just need to decide on the artwork.

[alexoshowo]

https://github.com/ppy/osu-resources/blob/26ac37d6d5bde86f85d2cca18cacbef6e30c8156/osu.Game.Resources/Textures/Backgrounds/registration.jpg
we can use this as placeholder/offline, but otherwise show a random artwork from recent art contest