fix: adapt backport for v4-next (no v4.2.0 version yet)

Adapt cherry-pick result for v4-next, which does not yet contain the
v4.2.0 versioned snapshot nor the operator v4.2.md source file.

- Revert misdirected rename targets in v4.1.2/operators/changelog/index.md
  and v2.1.11-ignition-sidebars.json (v4.2 entries point to files that do
  not exist on this branch).
- Drop the v4.2 entries from docs-operate/operators/reference/changelog/
  index.md and sidebars-operate.js for the same reason — including them
  would break the Docusaurus build. They should be added back when v4.2
  infrastructure (#22581 / #22612) is backported.

Kept:
- docs-operate/reference/changelog/v4.md content restore (core fix)
- v4.1.2/operators/reference/changelog/v4.md HA-guide link fix (the
  target file is high-availability.md on v4-next too, so the underscore
  link was already broken here).

Author: AztecBot

docs/docs-operate/operators/reference/changelog/index.md

@@ -11,19 +11,6 @@ This changelog documents all configuration changes, new features, and breaking c
 
 ## Version history
 
-### [v4.2.0](./v4.2.md)
-
-New features and configuration options for node operators.
-
-**Key changes:**
-- Blob retrieval improvements with unified retry loop
-
-**Migration difficulty**: Low
-
-[View full changelog →](./v4.2.md)
-
----
-
 ### [v4.x (Upgrade from Ignition)](./v4.md)
 
 Major upgrade from Ignition (v2.x) to Alpha (v4.x) with significant architectural changes.

docs/network_versioned_docs/version-v4.1.2/operators/reference/changelog/index.md

@@ -11,19 +11,6 @@ This changelog documents all configuration changes, new features, and breaking c
 
 ## Version history
 
-### [v4.2.0](./v4.2.md)
-
-New features and configuration options for node operators.
-
-**Key changes:**
-- Blob retrieval improvements with unified retry loop
-
-**Migration difficulty**: Low
-
-[View full changelog →](./v4.2.md)
-
----
-
 ### [v4.x (Upgrade from Ignition)](./v4.md)
 
 Major upgrade from Ignition (v2.x) to Alpha (v4.x) with significant architectural changes.

docs/network_versioned_sidebars/version-v2.1.11-ignition-sidebars.json

@@ -136,7 +136,6 @@
         "id": "operators/reference/changelog/changelog"
       },
       "items": [
-        "operators/reference/changelog/v4.2",
         "operators/reference/changelog/v4",
         "operators/reference/changelog/v2.0.2"
       ]

docs/sidebars-operate.js

@@ -145,7 +145,6 @@ const sidebars = {
         id: "operators/reference/changelog/changelog",
       },
       items: [
-        "operators/reference/changelog/v4.2",
         "operators/reference/changelog/v4",
         "operators/reference/changelog/v2.0.2",
       ],