[release-2.30] proxy: Fix the no_proxy variable (#13111)

* CI: add no_proxy regression test

* proxy: Fix the no_proxy variable

Since 2.29, probably due to a change in ansible templating, the no_proxy
variable is rendered as an array of character rather than a string.

This results in broken cluster in some case.

Eliminate the custom jinja looping to use filters and list flatteing +
join instead.
Also simplify some things (no separate tasks file, just use `run_once`
instead of delegating to localhost)

---------

Co-authored-by: Max Gautier <mg@max.gautier.name>

tests/files/rockylinux10-cilium.yml

@@ -13,3 +13,21 @@ kube_owner: root
 # Node Feature Discovery
 node_feature_discovery_enabled: true
 kube_asymmetric_encryption_algorithm: "ECDSA-P256"
+
+# Testing no_proxy setup
+# The proxy is not intended to be accessed at all, we're only testing
+# the no_proxy construction
+https_proxy: "http://some-proxy.invalid"
+http_proxy: "http://some-proxy.invalid"
+additional_no_proxy_list:
+  - github.com
+  - githubusercontent.com
+  - k8s.io
+  - rockylinux.org
+  - docker.io
+  - googleapis.com
+  - quay.io
+  - pkg.dev
+  - amazonaws.com
+  - cilium.io
+skip_http_proxy_on_os_packages: true