feat(supported-version): add user-defined kind (#28)

`kind` is a new input property for the `supported-version` action which
allows one to define what specific versions of Magento they support.

Currently, `kind` supports `latest`, `currently-supported`, and `custom`. See the
README for `supported-version` if you want more specifics

supported-version/src/matrix/get-matrix-for-kind.ts

@@ -0,0 +1,17 @@
+import { getMatrixForVersions } from "./get-matrix-for-versions";
+
+import latestJson from '../kind/latest.json';
+import currentlySupportedJson from '../kind/currently-supported.json';
+
+export const getMatrixForKind = (kind: string, versions: string = "") => {
+    switch(kind){
+        case 'latest': 
+          return getMatrixForVersions(latestJson);
+        case 'currently-supported':
+          return getMatrixForVersions(currentlySupportedJson);
+        case 'custom':
+          return getMatrixForVersions(versions.split(","))
+        default:
+          throw new Error(`Unreachable kind: ${kind} discovered, please report to the maintainers.`);
+      }
+}