Forms: Introduce new Primary, Secondary and Destructive buttons (#19973)

* Implement Label component

* Expose next-gen form components from grafana-ui under Forms namespace

* adding knobs to story, setting new variants and sizes

* handle next gen button in their own component

* removing duplication

* fix Thresholds test

* removing blank lines

* moving noUnusedLocals

* new button should not need theme

* remove not used export

* pseudo classes for focus state

* remove not used things

* use correct border radius

* extracting focus styles to commonStyles for reuse

* tidying up getButtonStyles

* Adding a few examples to the doc

* Adding props table

package.json

@@ -161,7 +161,7 @@
     "jest": "jest --notify --watch",
     "e2e-tests": "jest --runInBand --config=jest.config.e2e.js",
     "api-tests": "jest --notify --watch --config=devenv/e2e-api-tests/jest.js",
-    "storybook": "cd packages/grafana-ui && yarn storybook",
+    "storybook": "cd packages/grafana-ui && yarn storybook --ci",
     "storybook:build": "cd packages/grafana-ui && yarn storybook:build",
     "prettier:check": "prettier --list-different \"**/*.{ts,tsx,scss}\"",
     "prettier:write": "prettier --list-different \"**/*.{ts,tsx,scss}\" --write",