feat: add support for (nearly) any engine (#15)

* feat: add support for (nearly) any engine

* cache response and fixup data depth logic

* use starting slash as non-kv sentinel value

* add tests for custom engines

* improve docs and add descriptor of generic support

* update dist

action.test.js

@@ -17,8 +17,9 @@ describe('parseSecretsInput', () => {
         const output = parseSecretsInput('test key');
         expect(output).toContainEqual({
             secretPath: 'test',
-            secretKey: 'key',
+            secretSelector: 'key',
             outputName: 'KEY',
+            isJSONPath: false
         });
     });