Add way to override default spacing suggestions

[DanielBreiner]

If I undestand correctly, since v4, there is no way to override which spacing options are available - aside from explicitly custom values (e.g. p-[10px]), you can either:

• use --spacing (the default 0.25rem or your own value) and get the default suggestions (shown below)
• or you don't get any suggestions (if --spacing or --* is set to initial).

The default suggestions are 0, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 16, 20, 24, 28, 32, 36, 40, 44, 48, 52, 56, 60, 64, 72, 80, 96. Our team would like to change these options - remove some or add new ones.