Init MetricsWatcher during app startup

[igor-egorov]

Referenced issues

Description of the Change

MetricsWatcher was omitted from loading after code refactoring some time ago. This PR brings it back.

Possible Drawbacks

All the rest refactored out classes were tested on current master branch state and are initialized somewhere else, thus there is no need to init them in KagomeApplicationImpl::run().

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1. Code is formatted: Have you run your code through clang-format to ensure it adheres to the project's coding standards? [Yes|]
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3. Self-review: Have you reviewed your own code to ensure it is free of typos, syntax errors, logical errors, and unresolved TODOs or FIXME without linking to an issue? [Yes|]
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