Audit follow-up: decide on deprecated Camel components without drop-in replacements (paho/MQTTv3, splunk, json-patch)

## Background

The 4.21.0 deprecation audit (#2830, fixed in #2886) removed the deprecated *endpoint options* it found (`pulsar-sink` / `slack-sink`). It also found three Kamelets using deprecated **Camel components** that have **no safe drop-in replacement**, so they were intentionally left for a maintainer/PMC decision rather than a breaking change.

## Components needing a decision

- **`json-patch-action`** → `camel:json-patch` (deprecated): no replacement component exists in the Camel 4.21 catalog.
- **`mqtt-source`, `mqtt-sink`** → `camel:paho` (MQTT v3, deprecated): the only sibling is `camel:paho-mqtt5` (MQTT **v5** — a protocol change), and `mqtt5-source` / `mqtt5-sink` already provide v5. Migrating would break v3 users or duplicate the v5 Kamelets.
- **`splunk-sink`, `splunk-source`** → `camel:splunk` (deprecated): `splunk-hec` is publish-only and config-incompatible; `splunk-source` (search) has no HEC equivalent, and `splunk-hec-sink` already covers HEC publishing.

## Options per component
1. Deprecate the affected Kamelet(s) (e.g. label/annotate, document) and steer users to alternatives where they exist.
2. Accept the behavioural change (e.g. migrate `mqtt-*` to MQTT v5) — needs an upgrade-guide note.
3. Keep as-is until the component is actually removed upstream in Camel, then revisit.

No action is required in the catalog until Camel removes these components; this issue tracks the decision so the deprecations are not forgotten.

_AI-generated by Claude Code on behalf of Andrea Cosentino (@oscerd)_

Start with the deprecation audit in #2830 and its fix in #2886, then review the listed Kamelets and their Camel component mappings. Done means recording a maintainer or PMC decision for json-patch-action, mqtt-source/sink, and splunk-source/sink, with any required deprecation or upgrade-guide follow-up identified.

Written by the indexing model from the issue text.