Document the embed etcd configurations and their usage

We should add a new sub page to our [developer guide](https://etcd.io/docs/v3.6/dev-guide) to document how `GRPCAdditionalServerOptions` can be used for changing the default internal gRPC configuration.

```go
// GRPCAdditionalServerOptions is the additional server option hook
// for changing the default internal gRPC configuration. Note these
// additional configurations take precedence over the existing individual
// configurations if present. Please refer to
// https://github.com/etcd-io/etcd/pull/14066#issuecomment-1248682996
GRPCAdditionalServerOptions []grpc.ServerOption `json:"grpc-additional-server-options"`

```

See https://github.com/etcd-io/etcd/pull/14066#discussion_r1639280620