Release from operator repo

Prior to this commit, the helm-charts repo hosted downstream copies of the
redpanda, console, connectors[^1] and operator charts.

To release these charts, we would manually copy the trees into this repo and
rely on chart-releaser.

This process was quite unpleasant as it lead to many surprises from the
workflows in this repo and caused a good amount of confusion for contributors.

This commit removes the mirrored charts and replaces the release process with a
new GHA that pulls release information from the redpanda-operator repository.
chart-releaser is leveraged to update the index.yaml in the gh-pages branch as
usual.

In addition to the removal, a new README.md has been added as the previous
symlink to the redpanda chart's README.md is now dead.

[^1]: While the connectors chart technically exists in the redpanda-operator,
it's been moved to community maintenance as of the v25.1.1 redpanda release.
It's source is being left in place as it's been removed from newer operator
releases.

Author: chrisseto

.github/chart-releaser.nix

@@ -11,7 +11,7 @@
 
 buildGoModule rec {
   pname = "chart-releaser";
-  version = "1.6.0";
+  version = "1.8.1";
 
   # Don't run tests.
   doCheck = false;
@@ -21,10 +21,10 @@ buildGoModule rec {
     owner = "helm";
     repo = pname;
     rev = "v${version}";
-    hash = "sha256-rPNGg4nrDFIa1PAw3efFU/pQub33+QD0vNFu8kiU2/E=";
+    hash = "sha256-h1czHb/xK+kOEK4TJhMnwnLeVmQm52C8dTUy+fahJ90=";
   };
 
-  vendorHash = "sha256-zBVAER1RJy449GUndvQkG8R84vOuL+IN4exjETVHp9k=";
+  vendorHash = "sha256-nUqUtm7SUKNEITzFJ4gozlegqGtyiRNGKDyOqteGYTw=";
 
   postPatch = ''
     substituteInPlace pkg/config/config.go \