fix: update flash to play nicely with tailwind JIT purge

[superhawk610]

In order for Tailwind JIT to include classnames, they must be included in full somewhere in a source file included on the purge list. This means that string interpolation won't be included (see https://v2.tailwindcss.com/docs/just-in-time-mode, heading titled "Dynamic values").

This PR also updates the flash helper to use the error icon for error flash messages, in place of a red check mark.

[nickolaich]

I dare to suggest a change in approach and use css features:
instead of bg_class/button_class/text_class, add a root class to flash errors:
flash-error
flash-info
etc

and implement it at app.scss

.flash-error {
  @apply bg-red-50;
}
.flash-error button{
  @apply text-red-1 focus:ring-offset-red-50 focus:ring-red-1;
}

We can easily add later any type of flashes: success/warning etc.

and probably Tailwind JIT will catch them automatically.

[superhawk610]

@nickolaich that's a good idea, but crunch_berry doesn't ship any CSS files, so any styling has to be done inline. We could add those CSS rules into ecom_api, but then crunch_berry isn't self-contained. I'll start a discussion in the #crunch-berry-components channel in Slack to explore this idea further, though.