feat(elements): add light- & dark-mode configuration

[TobiasHeimGalindo]

Closes #1057

Theme switch example (highlighted green only for the accordion--expanded component currently):

https://github.com/inovex/elements/assets/81302108/56816cb5-db5c-4910-8171-c7dfaa5b49bc

Notes:

• Define new primary/neutral/alert colors in our global styles.scss
• Enable our inovex Elements components to be theme aware by using CSS variables ( var(--inovex-elements-p-1); instead of theme.$p-1;).
• Switch the css class in the landingpage and storybook to .inovex-elements-theme & .inovex-elements-theme-dark
• Disabled all features for production using isInDevEnvironment flag

TODOS for 100% light- & dark-mode support

1. Add a dark theme color pallete covering all our neutral, primary and alert colors to our global styles.scss in the elements package

2. Stencil Components: Switch to CSS variables for light- & dark theme support (enables theme-awareness at runtime)

3. Design two new Ino-Icons for theme switch on landingpage: sun & moon icon (light & dark ino-switch toggle)

[janivo]

TODO: check MDC mixin compatibility