feat: Pluto and kubeent plugin: find removed Kubernetes apiVersions with Pluto or kubent

[vyrti]

Problem

An upgrade is the worst time to learn that a workload still uses
extensions/v1beta1. Sofka can show the object, but not whether the
apiVersion it carries is deprecated, already removed, or has anywhere to go.

Proposal

One package, plugins/deprecated-apis/, wrapping the two tools that answer
this question. All three commands are read-only.

Command	Tool	Scans
:pluto-cluster	Pluto	The whole context.
:kubent-cluster	kubent	The whole context, including Helm v3 release manifests.
:pluto-resource	Pluto	The selected object, piped to pluto detect -.

Findings from either tool render the same way, grouped by what they cost:
removed with no replacement first, then removed, then deprecated.

Why both tools

They disagree, and the disagreement is the useful part. Pluto knows whether
an apiVersion is merely deprecated or already gone at the target version, and
checks components beyond Kubernetes such as cert-manager and Istio. kubent
reads Helm release manifests, so it finds a dead apiVersion stored in a
release that no live object uses any more. Install either one; each command
names the tool it needs.

[nklmilojevic]

Feel free to add this as an issue in sofka-plugins, I accept this proposal, but as sofka-plugin, not as core.