Update config schema to govern and document config properties not currently captured

[kriswest]

Is your feature request related to a problem? Please describe.
The following important config properties are not adequately documented in the Config schema or documentation and TypeScript types generated from it:

git-proxy/config.schema.json

Lines 44 to 55 in 292ecad

	"commitConfig": {
	"description": "Enforce rules and patterns on commits including e-mail and message",
	"type": "object"
	},
	"attestationConfig": {
	"description": "Customisable questions to add to attestation form",
	"type": "object"
	},
	"domains": {
	"description": "Provide domains to use alternative to the defaults",
	"type": "object"
	},

Describe the solution you'd like
All configuration settings should be covered in the schema (and hence generated documentation and typescript types)