CAMEL-23576: camel-jira - align Exchange header constant names with Camel naming convention

[oscerd]

Backport of #23417 onto camel-4.18.x (target 4.18.3).

Summary

Renames the Exchange header string values in JiraConstants from non-Camel-prefixed values (IssueKey, ProjectKey, IssueTransitionId, linkType, minutesSpent, …) to CamelJira<Name>, following the convention used across the rest of the Camel component catalog.

• Java field names (ISSUE_KEY, ISSUE_PROJECT_KEY, …) are unchanged → routes referencing the constants symbolically keep working.
• Routes using the literal string values must be updated → documented in the 4.18 upgrade guide as a potential breaking change.
• Generated Endpoint DSL header accessors on JiraHeaderNameBuilder renamed accordingly (issueKey() → jiraIssueKey(), …).
• Producer error messages and component docs updated for consistency.

Follows the rename pattern of CAMEL-23526 (camel-cxf), CAMEL-23522 (camel-mail), CAMEL-23461 (camel-aws-bedrock). Part of the global sweep tracked by CAMEL-23577.

Note on the upgrade guide

Per the project backport policy, the matching camel-4x-upgrade-guide-4_18.adoc entry on main is synced in a separate doc-sync PR.

Test plan

• mvn -DskipTests install in components/camel-jira on 4.18.x — catalog + docs regenerated cleanly; endpoint DSL regenerated.
• CI full reactor build.

Reported by Claude Code on behalf of Andrea Cosentino

[gnodet]

Clean backport of #23417 from main to camel-4.18.x. Verified:

• Original PR merged: #23417 merged on main on 2026-05-22, this backport targets camel-4.18.x for 4.18.3.
• Header renames are consistent: all 19 header string values correctly renamed from their old forms (IssueKey, ProjectKey, linkType, minutesSpent, etc.) to CamelJira* prefix following Camel naming convention. The internal JIRA_REST_CLIENT_FACTORY constant is correctly left untouched (not a @Metadata-annotated exchange header).
• Java field names unchanged: constants like ISSUE_KEY, ISSUE_PROJECT_KEY, etc. keep their symbolic names, so routes using the constants continue to work.
• Error messages updated: all producer error messages now reference the new header names.
• Tests are covered: all existing tests use the Java constants (not raw strings), so they automatically work with the new values.
• Docs updated: jira-component.adoc consistently uses new header names. The IssueDescription references (which never had a corresponding constant in JiraConstants) are correctly replaced with "The exchange body is used as the issue description" -- a minor doc improvement over the original PR.
• Upgrade guide: comprehensive entry under "Upgrading from 4.18.1 to 4.18.3" with a full mapping table and Endpoint DSL accessor rename list. Correctly placed in the right section.
• Generated files: catalog JSON and Endpoint DSL JiraEndpointBuilderFactory regenerated and consistent.
• CI: all checks green.
• Doc-sync note: the PR description correctly notes that the matching camel-4x-upgrade-guide-4_18.adoc entry on main will be synced in a separate doc-sync PR per project backport policy.

LGTM.

Claude Code on behalf of Guillaume Nodet