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>

package.json

@@ -28,7 +28,7 @@
   },
   "devDependencies": {
     "@actions/io": "^1.0.2",
-    "@actions/tool-cache": "^1.3.3",
+    "@actions/tool-cache": "^1.5.2",
     "@types/jest": "^25.1.4",
     "@types/node": "^12.12.31",
     "@types/semver": "^7.1.0",