Extract button component

[gtsiolis]

Problem to solve

There are around 60 instances of a button across the product, see <button> instances[1].

Currently, all buttons rely on the main button styles in index.css.

gitpod/components/dashboard/src/index.css

Lines 55 to 57 in 77b4d06

	button {
	@apply cursor-pointer px-4 py-2 my-auto bg-green-600 dark:bg-green-700 hover:bg-green-700 dark:hover:bg-green-600 text-gray-100 dark:text-green-100 text-sm font-medium rounded-md focus:outline-none focus:ring transition ease-in-out;
	}

It would be great to have a button component to cover some of the sizes, states, categories, variants, content, etc. and also support light / dark theme.

• Sizes: small, medium, block (full width) for Epic: Improve dashboard responsive layout #4050.
• Categories: disabled, loading, ...
• Categories: primary, secondary, ...
• Variants: confirm, default, danger, link, ...
• Content: label, Icon, ...

The need for a button component has been discussed briefly before a couple of times:

• No feedback when triggering prebuilds #5374 (comment)
• [dashboard] add button.gp-link CSS class #9641 (review)
• Add phone verification #12258 (comment)
• ...

See also relevant discussion in #16391 (comment). Cc @selfcontained