Add builder_confighub_endpoint to the config (#14)

## 📝 Summary

Add `builder_confighub_endpoint` to the config

## ⛱ Motivation and Context

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

## 📚 References

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which add value to the PR -->

---

## ✅ I have run these commands

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

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Signed-off-by: bakhtin <[email protected]>

testdata/get-configuration.json

@@ -14,7 +14,8 @@
         "builder_endpoint": "http://127.0.0.1:8645",
         "local_listen_addr": "0.0.0.0:443",
         "public_listen_addr": "0.0.0.0:5544",
-        "cert_hosts": "1.2.3.4,localhost,127.0.0.1"
+        "cert_hosts": "1.2.3.4,localhost,127.0.0.1",
+        "builder_confighub_endpoint": "http://127.0.0.1:7937"
     },
     "rbuilder": {
         "__version": "v0.1.0-26-g18875a4",