An option to make AdGuard Home install available updates on (re)starts

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### 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 (v0.108.0-b.5)
- [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
I know that the scenario where this feature would be useful is a bit narrow, but here goes:

Currently, in order to update AdGuard Home, one has to open the AGH GUI and click on a button that says "Update now", most likely to prevent unplanned server downtime. However, in cases where the AGH installation's owner is feeling fatigued, is busy with other activities, or has even forgot about the server, this can lead to AdGuard Home installations being potentially several months old and outdated.

### Proposed Solution
So I got a somewhat random fix for that scenario: What if there was an option in Settings → General Settings called *"Update on AdGuard Home startup"*, that would install available AGH updates whenever AGH itself or its service is started/restarted. The logic is that the server was already down, and can just as well spend an extra 10sec updating before going up again.

### Alternatives Considered
None that I can think of.

### Additional Information
Update lengths depend to some extent on the size of the query log. Until I reduced the log sizes on my server from 8 GB to circa 90 MB, updates that took more than a minute weren't uncommon. So that has to be added to consideration when implementing the solution above, on the assumption that a very narrow subcategory of end-users would be confused if it took more than 2min for AGH to start up.