What problem does this address?

In block.json setting the allowVerticalAlignment to true in the following way:

{
	"supports": {
		"layout": {
			"default": {
				"type": "flex"
			},
			"allowVerticalAlignment": true,
			"allowJustification": false,
			"allowOrientation": false,
			"allowInheriting": false
		}
	}
}

At the moment the default value of the vertical alignment is hardcoded here:

Based on the orientation it will be either set to center or top.

It would be useful to be able to set the default to a custom value, like for example bottom in the below case:

In the above case, the default position of the Next/Previous buttons for the Product Image Gallery is bottom, but the default vertical alignment set by Gutenberg is center.