Init Polish localization (#18419) (#18659)

Initial commit for Polish localization

* Translation style reviewed and improved by:
  Michał Sochoń <kaszpir@gmail.com>
  Karol Pucyński <kpucynski@gmail.com>
  with contribution from Wojciech Kocjan <wojciech@kocjan.org>

* Kubernetes slogan translated by Karol Pucyński
* Corectness of non-language-specific content reviewed and improved by:
  Tim Bannister <tim@scalefactory.com>

content/pl/docs/templates/index.md

@@ -0,0 +1,13 @@
+---
+headless: true
+
+resources:
+- src: "*alpha*"
+  title: "alfa"
+- src: "*beta*"
+  title: "beta"
+- src: "*deprecated*"
+  title: "wycofywane"
+- src: "*stable*"
+  title: "stabilne"
+---