Use GitHub releases to download python versions (#85)

This pull-request improves `setup-python` action to add ability to download specific version of Python on flight if it is not available by default.

**Details:**
`setup-python` action will download and install specific Python version from GitHub releases ([actions/python-versions](https://github.com/actions/python-versions/releases)) in case the version is not found in the local cache. All versions of Python available for installation are published in [actions/python-versions](https://github.com/actions/python-versions) repository.
All available versions are listed in the [version-manifest.json](https://github.com/actions/python-versions/blob/master/versions-manifest.json) file.

**Installation time:**

- Ubuntu / macOS: 10-20 seconds
- Windows: ~ 1 minute (mostly related to fact that we use MSI installer for Python on Windows)

Co-authored-by: MaksimZhukov <v-mazhuk@microsoft.com>
Co-authored-by: Konrad Pabjan <konradpabjan@github.com>
Co-authored-by: Brian Cristante <33549821+brcrista@users.noreply.github.com>

src/install-python.ts

@@ -0,0 +1,65 @@
+import * as path from 'path';
+import * as core from '@actions/core';
+import * as tc from '@actions/tool-cache';
+import * as exec from '@actions/exec';
+import {ExecOptions} from '@actions/exec/lib/interfaces';
+
+const AUTH_TOKEN = core.getInput('token');
+const MANIFEST_REPO_OWNER = 'actions';
+const MANIFEST_REPO_NAME = 'python-versions';
+export const MANIFEST_URL = `https://raw.githubusercontent.com/${MANIFEST_REPO_OWNER}/${MANIFEST_REPO_NAME}/master/versions-manifest.json`;
+
+const IS_WINDOWS = process.platform === 'win32';
+
+export async function findReleaseFromManifest(
+  semanticVersionSpec: string,
+  architecture: string
+): Promise<tc.IToolRelease | undefined> {
+  const manifest: tc.IToolRelease[] = await tc.getManifestFromRepo(
+    MANIFEST_REPO_OWNER,
+    MANIFEST_REPO_NAME,
+    AUTH_TOKEN
+  );
+  return await tc.findFromManifest(
+    semanticVersionSpec,
+    true,
+    manifest,
+    architecture
+  );
+}
+
+async function installPython(workingDirectory: string) {
+  const options: ExecOptions = {
+    cwd: workingDirectory,
+    silent: true,
+    listeners: {
+      stdout: (data: Buffer) => {
+        core.debug(data.toString().trim());
+      }
+    }
+  };
+
+  if (IS_WINDOWS) {
+    await exec.exec('powershell', ['./setup.ps1'], options);
+  } else {
+    await exec.exec('bash', ['./setup.sh'], options);
+  }
+}
+
+export async function installCpythonFromRelease(release: tc.IToolRelease) {
+  const downloadUrl = release.files[0].download_url;
+
+  core.info(`Download from "${downloadUrl}"`);
+  const pythonPath = await tc.downloadTool(downloadUrl, undefined, AUTH_TOKEN);
+  const fileName = path.basename(pythonPath, '.zip');
+  core.info('Extract downloaded archive');
+  let pythonExtractedFolder;
+  if (IS_WINDOWS) {
+    pythonExtractedFolder = await tc.extractZip(pythonPath, `./${fileName}`);
+  } else {
+    pythonExtractedFolder = await tc.extractTar(pythonPath, `./${fileName}`);
+  }
+
+  core.info('Execute installation script');
+  await installPython(pythonExtractedFolder);
+}