feat: introduce provider_id to sync service FetchAllFlags (#87)

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## This PR
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- introduces the `provider_id` field to the `FetchAllFlagsRequest`
message

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---------

Signed-off-by: James Milligan <james@omnant.co.uk>

Author: james-milligan

protobuf/sync/v1/sync_service.proto

@@ -6,7 +6,7 @@ option go_package = "flagd/grpcsync";
 
 // SyncFlagsRequest is the request initiating the sever-streaming rpc. Flagd sends this request, acting as the client
 message SyncFlagsRequest {
-  // Optional: A unique identifier for flagd  provider (grpc client) initiating the request. The server implementations
+  // Optional: A unique identifier for flagd provider (grpc client) initiating the request. The server implementations
   // can utilize this identifier to aggregate flag configurations and stream them to a specific client. This identifier
   // is intended to be optional. However server implementation may enforce it.
   string provider_id = 1;
@@ -47,7 +47,12 @@ message SyncFlagsResponse {
 }
 
 // FetchAllFlagsRequest is the request to fetch all flags. Flagd sends this request as the client in order to resync its internal state
-message FetchAllFlagsRequest {}
+message FetchAllFlagsRequest {
+  // Optional: A unique identifier for flagd provider (grpc client) initiating the request. The server implementations
+  // can utilize this identifier to aggregate flag configurations and stream them to a specific client. This identifier
+  // is intended to be optional. However server implementation may enforce it.
+  string provider_id = 1;
+}
 
 //  FetchAllFlagsResponse is the server response containing feature flag configurations
 message FetchAllFlagsResponse {