CAMEL-23575: docs - sync camel-mongodb-gridfs 4.18 upgrade-guide entry to main

[oscerd]

Summary

Doc-sync companion to the #23413 / CAMEL-23575 backport to camel-4.18.x (#23473).

Per the backport upgrade-guide policy in CLAUDE.md, the version-specific camel-4x-upgrade-guide-4_XX.adoc files for all release lines live on main as the canonical history. The code fix for CAMEL-23575 is backported to the camel-4.18.x maintenance branch (4.18.3), so the matching upgrade-guide entry must also be present in camel-4x-upgrade-guide-4_18.adoc on main — otherwise main's 4.18 guide drifts out of sync with what ships on 4.18.x.

This PR adds the === camel-mongodb-gridfs note to the "Upgrading from 4.18.1 to 4.18.3" section, documenting:

• the gridfs.* -> CamelGridFs* header constant value renames, and
• the cascading GridFsHeaderNameBuilder Endpoint DSL accessor renames.

Routes referencing the constants symbolically are unaffected; only routes using the literal string keys or the fluent builder methods need updating.

Related

• Main fix (4.21): CAMEL-23575: camel-mongodb-gridfs - align Exchange header constant names with Camel naming convention #23413 (merged, CAMEL-23575)
• Backport (4.18.x): [backport camel-4.18.x] CAMEL-23575: camel-mongodb-gridfs - align Exchange header constant names with Camel naming convention #23473

Docs-only change — no build required.

Prepared by Claude Code on behalf of Andrea Cosentino.

[gnodet]

Content looks good. The upgrade guide entry is an exact copy of the corresponding entry already in camel-4x-upgrade-guide-4_21.adoc (added by PR #23413 / commit 8f0b1ac), and the placement at the end of the "Upgrading from 4.18.1 to 4.18.3" section is correct.

I verified:

• All five header constant renames match the actual GridFsConstants.java changes on main (the old gridfs.* values -> new CamelGridFs* values).
• All five Endpoint DSL accessor renames match what was regenerated.
• AsciiDoc formatting is correct (heading level, bullet lists, backtick formatting).

One thing to address before merging: the PR currently shows a merge conflict (likely from other recent doc-sync PRs that touched the same file area). A rebase onto current main should resolve it cleanly.

Claude Code on behalf of Guillaume Nodet

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