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.spec.ts

@@ -0,0 +1,35 @@
+import { getMatrixForKind } from "./get-matrix-for-kind";
+
+describe('getMatrixForKind', () => {
+    it('returns a matrix for `latest`', () => {
+        const result = getMatrixForKind("latest");
+
+        expect(result.magento).toBeDefined();
+        expect(result.include).toBeDefined();
+    });
+
+    it('returns a matrix for `currently-supported`', () => {
+        const result = getMatrixForKind("currently-supported");
+
+        expect(result.magento).toBeDefined();
+        expect(result.include).toBeDefined();
+    });
+
+    it('returns a matrix for valid `custom`', () => {
+        const result = getMatrixForKind("custom", "magento/project-community-edition:2.3.7-p3");
+
+        expect(result.magento).toBeDefined();
+        expect(result.include).toBeDefined();
+    });
+
+    it('returns a matrix for valid multiple `custom`', () => {
+        const result = getMatrixForKind("custom", "magento/project-community-edition:2.3.7-p3,magento/project-community-edition:2.4.0");
+
+        expect(result.magento).toBeDefined();
+        expect(result.include).toBeDefined();
+    });
+
+    it('errors for invalid `custom``', () => {
+        expect(() => getMatrixForKind("custom")).toThrowError();
+    });
+})