Add DNS strategy in client settings

### Prerequisites

Please answer the following questions for yourself before submitting an issue. **YOU MAY DELETE THE PREREQUISITES SECTION.**

- [x] I am running the latest version
- [x] I checked the documentation and found no answer
- [x] I checked to make sure that this issue has not already been filed

### Problem Description

Now we can only choose DNS strategy, balance, parallel or fastest, in *DNS settings*. For a client, it is OK to set several upsteram DNS, but cannot choose DNS strategy.

It seems that the DNS strategy for a client maintain the same with general setting, but there are no tips about it in client settings.

### Proposed Solution

Make it possible to choose DNS strategy for a client.

### Alternatives Considered

Add tips in client's DNS settings about client's DNS strategy is same with general setting.