add new `GET /api/charts/:name` endpoint

The new endpoint will return a data view containing the chart configuration from Catalyst plus the default chart values.

Also added a couple refactors/fixes.

Returned JSON looks like:

{
	"name": "mediawiki",
	"description": "mediawiki and extensions",
	"gitRepo": "https://gitlab.wikimedia.org/repos/qte/catalyst/ci-charts",
	"directory": "mediawiki",
	"defaultValues": {
		"db": {
			"rootPassword": "secret",
			"rootUsername": "root"
		},
		"extensions": {
			"echo": {
				"enable": false,
				"ref": "master"
			},
			"thanks": {
				"enable": false,
				"ref": "master"
			}
		},
		"mediawikiCore": {
			"ingress": null,
			"password": "dockerpass",
			"ref": "master",
			"siteName": "VanillaWiki",
			"user": "Admin"
		},
		"skins": {
			"timeless": {
				"enable": false,
				"ref": "master"
			}
		}
	}
}

Where the first portion of the message is the chart configuration from catalyst, and the second portion the values.yaml from the chart itself.

Bug: T363852