chore(docs): sync 4.18 and 4.14 upgrade guides with backported entries

[oscerd]

Summary

The 4.18 and 4.14 upgrade guides on `main` had drifted out of sync with their counterparts on the maintenance branches. Backport PRs for CAMEL-23373 (camel-jms) and CAMEL-23414 (camel-hazelcast) updated only the maintenance branches; the entries never made it back to `main`'s copies.

This PR adds the missing entries so the canonical upgrade guides on `main` reflect what actually shipped (or is shipping) in 4.18.3 and 4.14.8.

Changes

`camel-4x-upgrade-guide-4_18.adoc` (under "Upgrading from 4.18.1 to 4.18.3")

• Add `=== camel-jms` (CAMEL-23373, on camel-4.18.x via CAMEL-23373: camel-jms - Disable ObjectMessage by default #22866 / 844bbf8)
• Add `=== camel-hazelcast` (CAMEL-23414, on camel-4.18.x via [backport camel-4.18.x] CAMEL-23414: Allow customization of SerializationConfig on managed Hazelcast instances #22946 / 5caf436)
• Existing `=== camel-core` (DefaultHeaderFilterStrategy lowercase) preserved
• Section title kept as-is (not aligned with the maintenance branch's "4.18.2 to 4.18.3")

`camel-4x-upgrade-guide-4_14.adoc` (under section for 4.14.8)

• Fix typo: section title `Upgrading from 4.14.3 to 4.18.8` → `Upgrading from 4.14.3 to 4.14.8`
• Add `=== camel-jms` (CAMEL-23373, on camel-4.14.x via [backport camel-4.14.x] CAMEL-23373: camel-jms - Disable ObjectMessage by default #22920 / 75d7991)
• Add `=== camel-hazelcast` (CAMEL-23414, on camel-4.14.x via [backport camel-4.14.x] CAMEL-23414: Allow customization of SerializationConfig on managed Hazelcast instances #22955 / 974a11b)
• Existing `=== camel-core` preserved

Not included

• `camel-sjms / camel-sjms2` (CAMEL-23409) is intentionally omitted for the 4.18.3 entry: PR [backport camel-4.18.x] CAMEL-23409: camel-sjms - Disable ObjectMessage by default #22968 (the 4.18.x backport) is still open. A follow-up will add it once that lands.
• Other doc divergences on the 4.14.5/4.14.6/etc sections are out of scope; this PR only catches up on the 4.18.3 and 4.14.8 sections.

Test plan

Documentation-only change. No build verification needed beyond the AsciiDoc preview.

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Claude Code on behalf of Andrea Cosentino

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