Make kcidb-schema output older schema versions on request

[spbnick]

No description provided.

[spbnick]

The kcidb-schema tool available after installing KCIDB supports outputting the latest version of the schema only. Like this:

$ kcidb-schema
{   
    "title": "kcidb",
    "description": "Kernel CI report data. ...",
    "type": "object",
    "properties": {
        "version": {
            "type": "object",
            "properties": {
                "major": {
                    "type": "integer",
...

Make it accept a positional argument specifying the major version of the schema to output JSON for. Like this:

$ kcidb-schema 3
{   
    "title": "kcidb",
    "description": "Kernel CI report data. ...",
    "type": "object",
    "properties": {
        "version": {
            "type": "object",
            "properties": {
                "major": {
                    "type": "integer",
...

[spbnick]

Fixed in #231