Install files to executable directory instead of working directory

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### Prerequisites

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- [x] I am running the latest version
- [x] I checked the documentation and found no answer
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### Problem Description
The updater currently installs files to the working directory: https://github.com/AdguardTeam/AdGuardHome/blob/master/internal/updater/updater.go#L249-L274
By default the working directory matches the executable directory, but using the `-w, --work-dir` option changes this, so that files are tried to be installed to the wrong directory.

### Proposed Solution
Instead of deriving the target directory from the working directory, the updater could use the location of the running AdGuard Home executable itself, so that the working directory can be changed without breaking the updater.

### Alternatives Considered
I'm not sure whether there is already some kind of bin dir implemented that can be used, or otherwise if there is a different way to change the location of config and data without breaking the updater. But it doesn't seem intended to me that `-w, --work-dir` inherently breaks it.

### Additional Information
We use the `-w, --work-dir` option in our implementation to separate the static binary and install files from variable user data and config, but the updater then fails.