refactor(updater): smart message generation (part 3 of shoutrrr support)

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 95.31250% with 9 lines in your changes missing coverage. Please review.

Project coverage is 89.20%. Comparing base (dc18a68) to head (bc1697d).

Files	Patch %	Lines
cmd/ddns/ddns.go	0.00%	9 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #762 +/- ## ========================================== + Coverage 88.40% 89.20% +0.80% ========================================== Files 48 51 +3 Lines 2000 2112 +112 ========================================== + Hits 1768 1884 +116 + Misses 210 206 -4 Partials 22 22 ``` | [Flag](https://app.codecov.io/gh/favonia/cloudflare-ddns/pull/762/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=favonia) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/favonia/cloudflare-ddns/pull/762/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=favonia) | `89.20% <95.31%> (+0.80%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=favonia#carryforward-flags-in-the-pull-request-comment) to find out more.

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