Document Async POSIX Signal Control in frontend user docs

[AdamBrouwersHarries]

Following some discussion around documenting the POSIX signal control feature, it seems like this is a better place for it to live. This PR adds documentation on using POSIX signals to control the profiler to the "advanced topics" section of the documentation.

[codecov[bot]]

Codecov Report

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

Project coverage is 88.48%. Comparing base (579e273) to head (ce61ec8). Report is 21 commits behind head on main.

:exclamation: Current head ce61ec8 differs from pull request most recent head 17483fa

Please upload reports for the commit 17483fa to get more accurate results.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #5013 +/- ## ======================================= Coverage 88.48% 88.48% ======================================= Files 304 304 Lines 27393 27393 Branches 7400 7400 ======================================= Hits 24240 24240 Misses 2931 2931 Partials 222 222 ```

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