Add schemas

[alvaromartmart]

It is possible to use JSON schemas to validate the YML files, which would make it much easier to author these.

I don't have too much experience with YML validation tooling, but I have managed to set up some basic integration in VSCode, involving:

• Creating a seqera-kit.schema.json declaring the valid properties for organizations, e.g.

{
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "title": "seqerakit yml file",
    "type": "object",
    "properties": {
        "organizations": {
            "description": "Organizations",
            "type": "array",
            "items": {
                "type": "object",
                "properties": {
                    "name": {
                        "type": "string",
                        "description": "Name of the organization"
                    },
                    "full-name": {
                        "type": "string",
                        "description": "Full name"
                    },
                    "description": {
                        "type": "string",
                        "description": "Description of the organization"
                    },
                    "location": {
                        "type": "string",
                        "description": "Description of the organization"
                    },
                    "website": {
                        "type": "string",
                        "description": "Website"
                    },
                    "overwrite": {
                        "type": ["boolean", "string"],
                        "description": "Overwrite the organization if it already exists"
                    }
                },
                "required": ["name"]
            }
        }
    }
}

• Telling VSCode which local json.schema file to use to validate specific .yml files:

	"settings": {
		"yaml.schemas": {
			"file:///seqera-kit.schema.json": "seqera-kit/**.yml"
		},