Add config for System API (#21)

## 📝 Summary
Add support for System API configuration

## ⛱ Motivation and Context

<!--- Why is this change required? What problem does it solve? -->

## 📚 References


Companion PRs:
- flashbots/meta-evm#44
- flashbots/meta-confidential-compute#29

---

## ✅ I have run these commands

* [x] `make lint`
* [x] `make test`
* [x] `go mod tidy`

Signed-off-by: bakhtin <a@bakhtin.net>

testdata/get-configuration.json

@@ -125,5 +125,10 @@
         "output_cw_log_group_name": "multioperator-builder",
         "aws_access_key_id": "xxx",
         "aws_secret_access_key": "xxx"
+    },
+    "system_api": {
+        "__version": "v0.7.0",
+        "basic_auth_secret_salt": "xxx",
+        "basic_auth_secret_hash": "xxx"
     }
 }