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-versions.ts

@@ -0,0 +1,21 @@
+import { GithubActionsMatrix, MagentoMatrixVersion } from "./matrix-type";
+import compositeVersionJson from '../versions/composite.json';
+import individualVersionJson from '../versions/individual.json';
+
+const knownVersions : Record<string, MagentoMatrixVersion> = {...individualVersionJson, ...compositeVersionJson };
+
+/**
+ * Computes the Github Actions Matrix for given versions of Magento
+ */
+export const getMatrixForVersions = (versions: string[]): GithubActionsMatrix => {
+    return versions.reduce((acc, current): GithubActionsMatrix => {
+        if(knownVersions[current] === undefined){
+            throw new Error("Unknown version while computing matrix");
+        }
+
+        return {
+            magento: [...acc.magento, current],
+            include: [...acc.include, knownVersions[current]]
+        }
+    }, {magento: [], include: []});
+}