Split site-specific-settings doc

[hmpf]

Closes #802

Move the howto to an actual separate howto page.

[sonarcloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

See analysis details on SonarCloud

[codecov-commenter]

Codecov Report

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

Project coverage is 84.77%. Comparing base (7f894f4) to head (1cbde5d).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #820 +/- ## ======================================= Coverage 84.77% 84.77% ======================================= Files 76 76 Lines 3835 3835 ======================================= Hits 3251 3251 Misses 584 584 ```

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Test results

       7 files     616 suites   23m 6s :stopwatch:    488 tests    487 :heavy_check_mark: 1 :zzz: 0 :x: 3 416 runs  3 409 :heavy_check_mark: 7 :zzz: 0 :x:

Results for commit 1cbde5d2.