missing documentation for `machineLearningApproachType`

[jkowalleck]

documentation for machineLearningApproachType is insufficient/missing

XML schema: all cases have the documentation text "TODO"
https://github.com/CycloneDX/specification/blame/299209abd9531d808e0cc4235e77a7c4b1b53d96/schema/bom-1.5.xsd#L3022-L3050

JSON schema: has no case documentation at all

specification/schema/bom-1.5.schema.json

Lines 2457 to 2468 in 299209a

	"type": {
	"type": "string",
	"title": "Learning Type",
	"description": "Learning types describing the learning problem or hybrid learning problem.",
	"enum": [
	"supervised",
	"unsupervised",
	"reinforcement-learning",
	"semi-supervised",
	"self-supervised"
	]
	}