feat(): add support for github provided jwt auth (#257)

* fix: update `privateKeyRaw` condition

* fix: add `contents: read` permission

* fix: get token via `@actions/core`

- Update README
- Switch to use `getIDToken` method for Github token retrieval
- Bump `@actions/core` to 1.6.0
- Add `jwtGithubAudience` input
- Remove unnecessary code

* fix: add description for `jwtGithubAudience`

* fix: move default value for `jwtGithubAudience` to `action.yml`

* docs: fix typo in README & grammar

* test: add tests

* fix: reset `dist/index.js`

* fix: remove default value for `jwtGithubAudience` from `action.yml`

* fix: reset `dist/index.js`

* fix: reset `dist/index.js`

package.json

@@ -52,7 +52,7 @@
         "@actions/core": ">=1 <2"
     },
     "devDependencies": {
-        "@actions/core": "^1.2.3",
+        "@actions/core": "^1.6.0",
         "@types/got": "^9.6.11",
         "@types/jest": "^26.0.13",
         "@zeit/ncc": "^0.22.3",