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

[oscerd]

Backport of #23417 onto camel-4.14.x (target 4.14.8).

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 4.14 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_14.adoc entry on main is synced in a separate doc-sync PR.

Test plan

• mvn -DskipTests install in components/camel-jira on 4.14.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. Verified:

• Original PR is merged on main (3240a17).
• All 20 header string values consistently renamed with the CamelJira prefix.
• Internal constants (ACCESS_TOKEN, VERIFICATION_CODE, PRIVATE_KEY, CONSUMER_KEY, JIRA_REST_CLIENT_FACTORY) are correctly left unchanged — they are configuration keys, not Exchange headers.
• Upgrade guide entry placed correctly under "Upgrading from 4.14.7 to 4.14.8" with a complete old→new mapping table and Endpoint DSL accessor rename list.
• Tests all reference headers via Java constants (ISSUE_KEY, ISSUE_PROJECT_KEY, etc.), so no test changes needed — confirmed by inspecting the test sources on the branch.
• Producer error messages updated to reference the new header names.
• Generated catalog JSON and Endpoint DSL JiraHeaderNameBuilder are regenerated.
• Component docs (jira-component.adoc) updated; the stale IssueDescription header references are correctly replaced with "The exchange body is used as the issue description" (no such constant existed).
• Doc-sync PR for main's camel-4x-upgrade-guide-4_14.adoc is tracked separately per the backport-upgrade-guide policy — noted in the PR description.

LGTM.

Claude Code on behalf of Guillaume Nodet