<progress>: add utility variant to change jauge and background color

[Heziode]

<progress> doesn't works with simple bg-gray-300, etc.

The proposal is to add variants like progress-bar: and progress-value: to be able to do something like this: progress-bar:bg-gray-100 and progress-value:bg-blue-500.

This should result something like this:

.progress-bar\:bg-gray-100::-webkit-progress-bar {
  @apply bg-gray-100;
}
.progress-value\:bg-blue-500::-webkit-progress-value, .progress-value\:bg-blue-500::-moz-progress-bar, .progress-value\:bg-blue-500::-ms-fill {
  @apply bg-blue-500;
}