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/index.ts

@@ -0,0 +1,20 @@
+import * as core from '@actions/core';
+import { validateOrError } from './kind/compute-kind';
+import { getMatrixForKind } from './matrix/get-matrix-for-kind';
+
+
+export async function run(): Promise<void> {
+  try { 
+    const kind = core.getInput("kind");
+    validateOrError(kind);
+
+    const customVersions = core.getInput("custom_versions");
+
+    core.setOutput('matrix', getMatrixForKind(kind, customVersions));
+  } 
+  catch (error) {
+    core.setFailed(error.message);
+  }
+}
+
+run()