Handle composable bake attributes

[crazy-max]

Atm we expect csv values when parsing the raw definition:

actions-toolkit/src/types/buildx/bake.ts

Lines 26 to 47 in 8e47567

	export interface Target {
	args?: Record<string, string>;
	attest?: Array<string>;
	'cache-from'?: Array<string>;
	'cache-to'?: Array<string>;
	context: string;
	contexts?: Record<string, string>;
	dockerfile: string;
	'dockerfile-inline'?: string;
	labels?: Record<string, string>;
	'no-cache'?: boolean;
	'no-cache-filter'?: Array<string>;
	output?: Array<string>;
	platforms?: Array<string>;
	pull?: boolean;
	secret?: Array<string>;
	'shm-size'?: string;
	ssh?: Array<string>;
	tags?: Array<string>;
	target?: string;
	ulimits?: Array<string>;
	}

With work being done to handle composable bake attributes in next Buildx 0.19.0 (docker/buildx#2758), we need to adapt and handle them correctly here.

cc @tonistiigi @jsternberg