clarify one-time v0.17.0 chart-restructuring migration vs. routine upgrades

The [Upgrade Guide](https://kserve.github.io/website/docs/next/install/upgrade-guide) doesn't clearly distinguish between :

1. A one-time migration needed to move *onto* the v0.17.0 chart layout (CRD-annotation/ownership etc.)
2. Ordinary upgrades *between* versions that are already on that layout (e.g. v0.17.0 → v0.18.0 → v0.19.0)

The "General Upgrade Process" section currently reads:

> For v0.17.0 and later, the Helm chart architecture has been completely restructured... you must follow the specific migration steps outlined in the v0.17.0 section below.

The ambiguity is compounded by the migration steps themselves living under a "v0.16.0 to v0.17.0" heading while their example commands target `--version v0.18.0`.

**Suggested fix:** split the guide into something like "One-time migration: moving onto the v0.17.0+ chart layout" (current steps, framed explicitly as a single historical transition) and "Routine upgrades between split-chart versions" (a short section showing the plain `helm upgrade --reuse-values` pattern per chart, with a tip to confirm current chart names via `helm list -n kserve` first).

Start in the linked Upgrade Guide and compare the General Upgrade Process with the v0.16.0 to v0.17.0 migration section and its example commands. Separate the one-time v0.17.0+ chart-layout migration from routine split-chart upgrades, document the plain helm upgrade --reuse-values pattern, and include checking current chart names with helm list -n kserve.

Written by the indexing model from the issue text.