[Docs] French translation of Complete Newbs Guide (#6901)

* Translated _summary.md + newbs.md

* Translated news_best_practices.md in French

* Translated newbs_building_firmware_configurator.md in French

* Translated the file newbs_building_firmware.md in French

* Translated page newbs_flashing.md in French

* Translated the page newbs_getting_started.md in French

* Translated the page newbs_learn_more_resources.md in French

* Translated the page newbs_testing_debugging.md in French

* Change translation of split from 'séparé' to 'scindé'

* Adding the lang file for gitbook and some others tranme other translation

* Correcting typos after Gimly's review

* Some others sections on the summary

* Fix first comments from @zekth

* Fix some issues from @4sStylZ

* Fix other issues from @4sStylZ

* Fix weird phrase

* Replaced all uses of  'téléverser' by 'flash'

* Replaced all planches by board

* Fix other PR comments

* Fix comment

docs/_langs.md

@@ -1,3 +1,4 @@
 - Translations
   - [:uk: English](/)
-  - [:cn: 中文](/zh-cn/)
+  - [:cn: 中文](/zh-cn/)
+  - [:fr: Français](/fr-fr/)