[UPDATE] Restore the previously removed API for etcd/grpc compatibility/update

[Alanxtl]

Description

The API / behavior was originally removed during the changes in:

• refactor: remove grpc.WithBlock() from etcd client dubbogo/gost#131

Later, we found this caused downstream compatibility problems for Dubbo-Go:

• [BUG] gost 最新的版本里面 grpc.WithBlocks 函数被删除，导致 dubbo-go 的单元测试失败 #3070

In particular, removing the grpc.WithBlock()-related behavior in gost affected the initialization semantics along this dependency chain:

dubbo-go -> gost -> etcd/clientv3 -> grpc

As discussed in #3070, this broke the expected behavior in the etcd registry path and caused unit test failures in Dubbo-Go.

Now the upstream etcd side has already updated the related implementation / discussion:

• grpc.DialOption have marked as deprecated in grpc, Is there any plan to replace it in clientv3.config ? etcd-io/etcd#20910
• grpc.DialOption have marked as deprecated in grpc, Is there any plan to replace it in clientv3.config ? etcd-io/etcd#20910 (comment)

So I think it is time to add this API / behavior back in gost.

Motivation

The original removal was understandable at that time, but it introduced real downstream compatibility issues.

Since the upstream dependency has now moved forward, restoring this API / behavior would help downstream projects such as Dubbo-Go remove temporary compatibility workarounds and recover the expected client initialization semantics.

References

• Original removal: refactor: remove grpc.WithBlock() from etcd client dubbogo/gost#131
• Compatibility regression discussion: [BUG] gost 最新的版本里面 grpc.WithBlocks 函数被删除，导致 dubbo-go 的单元测试失败 #3070
• Upstream etcd update: grpc.DialOption have marked as deprecated in grpc, Is there any plan to replace it in clientv3.config ? etcd-io/etcd#20910