feat: add splashless option to suppress splash screen on start

[jtackaberry]

This PR adds a ui.splashless option and corresponding --splashless flag to suppress the K9s startup splash screen. The default behavior is to continue showing the splash screen.

Fixes #1911

[sttts]

Thank you. This is how it should be. Have switched to your branch.

[alexellis]

This seems more like a feature for k9s-pro or sponsors? OSS is tough, we need to support maintainers for the value they create for us.

[sttts]

Thanks @alexellis for pointing me at the sponsorships. Wasn't aware. Done.

[jtackaberry]

OSS is tough, we need to support maintainers for the value they create for us.

I'd certainly see your point if it was a donation nag screen, or something that was obviously benefiting the maintainers, but it's literally just this:

Is it really a value to the maintainers for users to see this at each launch?

[144mb]

This seems more like a feature for k9s-pro or sponsors?

Please don't make OSS software crippleware. This hurts everyone. It's such a bad pattern. I know the guy recommending this is putting even more controversial restrictions on the users of some of his OSS projects, but that doesn't make it any better.

(This is not meant against maintainers. For years I have been given ca. 2% of my salary after taxes to OSS projects. And have rooted at every place that I have worked for buying commercial support and OSS based products. I don't sponsor this project as I currently don't use k8s, but will give at least a one time donation once it becomes relevant to me).