Introduce STS client grants API and OPA policy integration (#6168)

This PR introduces two new features

- AWS STS compatible STS API named AssumeRoleWithClientGrants

```
POST /?Action=AssumeRoleWithClientGrants&Token=<jwt>
```

This API endpoint returns temporary access credentials, access
tokens signature types supported by this API

  - RSA keys
  - ECDSA keys

Fetches the required public key from the JWKS endpoints, provides
them as rsa or ecdsa public keys.

- External policy engine support, in this case OPA policy engine

- Credentials are stored on disks

docs/config/config.sample.json

@@ -1,5 +1,5 @@
 {
-    "version": "29",
+    "version": "30",
     "credential": {
         "accessKey": "USWUXHGYZQYFYFFIT3RE",
         "secretKey": "MOJRH0mkL1IPauahWITSVvyDrQbEEIwljvmxdq03"
@@ -132,5 +132,27 @@
                 "password": ""
             }
         }
+    },
+    "logger": {
+        "console": {
+            "enabled": true
+        },
+        "http": {
+            "1": {
+                "enabled": false,
+                "endpoint": ""
+            }
+        }
+    },
+    "openid": {
+        "jwks": {
+            "url": ""
+        }
+    },
+    "policy": {
+        "opa": {
+            "url": "",
+            "authToken": ""
+        }
     }
 }