Fix formatting on UISP import notification slack messages

[Andrew-Dickinson]

Fixes an issue where the slack messages have really bad formatting due to the fact that newlines aren't allowed inside of bolded text.

Also removes some explanatory text that is confusing in most contexts, and should be obvious in the contexts where it is needed

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 94.11%. Comparing base (0a2eb83) to head (d2368b0). Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #709 +/- ## ======================================= Coverage 94.11% 94.11% ======================================= Files 82 82 Lines 3416 3418 +2 ======================================= + Hits 3215 3217 +2 Misses 201 201 ```

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