feat(nix): update NixOS version to 26.05 (#5350)

* feat(nix): update NixOS version to 26.05

* feat(nix): use Erlang 27 as 26 is not included in 26.05 anymore

* fix(nix): remove now-removed node2nix package from devenv

* feat(nix): add grafanaSecretKeyFile to apply now mandatory secret_key for Grafana

* docs: update changelog

Author: JakobLichterfeld

CHANGELOG.md

@@ -71,6 +71,7 @@
 - build(deps): update flake.lock (#5342 - @JakobLichterfeld)
 - build(deps): bump webpack-dev-server from 5.2.3 to 5.2.4 in /website (#5343)
 - sec(deps): add ws override to version 8.20.1 in /website (#5344 - @JakobLichterfeld)
+- feat(nix): update NixOS version to 26.05 (#5350 - @JakobLichterfeld)
 
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