backend: downgrade protoreflect to v1.14 (#772)

Due to an issue in the latest protoreflect lib a panic was
thrown when parsing protobuf schemas that used an import.

backend/go.mod

@@ -21,7 +21,7 @@ require (
 	github.com/hamba/avro/v2 v2.13.0
 	github.com/jarcoal/httpmock v1.0.8
 	github.com/jcmturner/gokrb5/v8 v8.4.4
-	github.com/jhump/protoreflect v1.15.1
+	github.com/jhump/protoreflect v1.14.1
 	github.com/knadh/koanf v1.5.0
 	github.com/mitchellh/mapstructure v1.5.0
 	github.com/prometheus/client_golang v1.15.1

backend/go.sum

@@ -346,6 +346,12 @@ github.com/jcmturner/gokrb5/v8 v8.4.4/go.mod h1:1btQEpgT6k+unzCwX1KdWMEwPPkkgBtP
 github.com/jcmturner/rpc/v2 v2.0.3 h1:7FXXj8Ti1IaVFpSAziCZWNzbNuZmnvw/i6CqLNdWfZY=
 github.com/jcmturner/rpc/v2 v2.0.3/go.mod h1:VUJYCIDm3PVOEHw8sgt091/20OJjskO/YJki3ELg/Hc=
 github.com/jessevdk/go-flags v1.5.0/go.mod h1:Fw0T6WPc1dYxT4mKEZRfG5kJhaTDP9pj1c2EWnYs/m4=
+github.com/jhump/gopoet v0.0.0-20190322174617-17282ff210b3/go.mod h1:me9yfT6IJSlOL3FCfrg+L6yzUEZ+5jW6WHt4Sk+UPUI=
+github.com/jhump/gopoet v0.1.0/go.mod h1:me9yfT6IJSlOL3FCfrg+L6yzUEZ+5jW6WHt4Sk+UPUI=
+github.com/jhump/goprotoc v0.5.0/go.mod h1:VrbvcYrQOrTi3i0Vf+m+oqQWk9l72mjkJCYo7UvLHRQ=
+github.com/jhump/protoreflect v1.11.0/go.mod h1:U7aMIjN0NWq9swDP7xDdoMfRHb35uiuTd3Z9nFXJf5E=
+github.com/jhump/protoreflect v1.14.1 h1:N88q7JkxTHWFEqReuTsYH1dPIwXxA0ITNQp7avLY10s=
+github.com/jhump/protoreflect v1.14.1/go.mod h1:JytZfP5d0r8pVNLZvai7U/MCuTWITgrI4tTg7puQFKI=
 github.com/jhump/protoreflect v1.15.1 h1:HUMERORf3I3ZdX05WaQ6MIpd/NJ434hTp5YiKgfCL6c=
 github.com/jhump/protoreflect v1.15.1/go.mod h1:jD/2GMKKE6OqX8qTjhADU1e6DShO+gavG9e0Q693nKo=
 github.com/jmespath/go-jmespath v0.4.0/go.mod h1:T8mJZnbsbmF+m6zOOFylbeCJqk5+pHWvzYPziyZiYoo=