CAMEL-23531: Fix Jackson 2.x/3.x dataformat doc collisions

[ammachado]

Description

Fixes CAMEL-23531.

The Jackson 2.x and 3.x dataformat lines share the same DSL name (jackson, jacksonXml, avroJackson, protobufJackson) so a runtime can drop in either variant transparently. The doc pipeline flattened both variants to the same destination filename, so the second symlink silently overwrote the first and only one entry appeared in the
dataformats nav.

Disambiguate at the doc layer only — runtime catalog and DSL behaviour are unchanged:

• Rename the per-module <name>-dataformat.adoc source files with a 2 / 3 suffix in all eight Jackson modules.
• Append the major-version suffix to the rendered .adoc title in UpdateReadmeMojo (driven by the artifactId), and look up the renamed page filename via the same suffix. The dataformat JSON title stays unsuffixed, so the catalog and dataFormatJSonSchema API keep their existing values.
• Detect destination-basename collisions in PrepareDocSymlinksMojo and disambiguate Jackson-family .json symlinks via the same artifact rule. Any unresolvable collision now fails the build loudly instead of silently overwriting one source.
• Regenerate the dataformats nav, page symlinks, JSON example symlinks, and per-module readme headers; both variants now appear with distinct titles (e.g. JSON Jackson 2 / JSON Jackson 3).
• Document the page renames in the 4.21 upgrade guide. No :page-aliases: created.

Target

• I checked that the commit is targeting the correct branch (Camel 4 uses the main branch)

Tracking

• If this is a large change, bug fix, or code improvement, I checked there is a JIRA issue filed for the change (usually before you start working on it).

Apache Camel coding standards and style

• I checked that each commit in the pull request has a meaningful subject line and body.
• I have run `mvn clean install -DskipTests` locally from root folder and I have committed all auto-generated changes.

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Claude Opus 4.7 on behalf of Adriano Machado

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🧪 CI tested the following changed modules:

• components/camel-jackson-avro
• components/camel-jackson-protobuf
• components/camel-jackson
• components/camel-jackson3-avro
• components/camel-jackson3-protobuf
• components/camel-jackson3
• components/camel-jackson3xml
• components/camel-jacksonxml
• docs
• tooling/maven/camel-package-maven-plugin

ℹ️ Dependent modules were not tested because the total number of affected modules exceeded the threshold (50). Use the test-dependents label to force testing all dependents.

Build reactor — dependencies compiled but only changed modules were tested (10 modules)

• Camel :: Docs
• Camel :: Jackson
• Camel :: Jackson 3
• Camel :: Jackson 3 Avro
• Camel :: Jackson 3 Protobuf
• Camel :: Jackson 3 XML
• Camel :: Jackson Avro
• Camel :: Jackson Protobuf
• Camel :: Jackson XML
• Camel :: Maven Plugins :: Camel Maven Package

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