Please enhance the DNS cache settings

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### Prerequisites

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

### Problem Description

When I used Adguard Home, I opened the "cache_optimistic" option, and I occasionally wondered how much the current DNS cache was used in order to increase the cache size in time when the cache was exhausted.

### Proposed Solution

Display the specific size of current DNS cache is used in the web interface.
And provide the function of refreshing DNS cache.

### Additional Information