0.9.19 General modernisation

Upgrade dependencies and add comprehensive parameter validation

Major Changes:

• Migration from old style maven doclets to modern annotations

  • Changes:
  • Remove @goal, @phase, @parameter, @required Javadoc tags
  • Add @mojo, @parameter, @LifecyclePhase Java annotations
  • Update ReleaseVersionMojo, CreateNewVersionMojo, GenerateReleaseNotesMojo

  This resolves the "unknown tag" errors that were blocking the Maven
  release process and GitHub Actions workflow.

  Fixes Javadoc generation for Maven Central deployment.

• Upgrade Java baseline requirement from Java 8 to Java 21, mainly due to atlassian jira client moving baseline to Java 21.

• Update all Maven plugin dependencies to latest versions

• Update Jira REST client to 7.0.1 and Fugue to 6.1.2
  Add extensive parameter validation tests with edge case coverage

New Documentation:

• Add PARAMETER_VALIDATION.md documenting all parameter requirements
• Add unit test README explaining test structure and patterns

Testing Improvements:

• Add ParameterValidationTest with comprehensive coverage
• Add TestAbstractJiraMojo helper class for validation testing
• Test empty strings, null values, and authentication combinations
• Update AllJiraTests suite to include new tests

Dependencies:

• Keep Mockito at 4.x with comment explaining Java 11 baseline requirement
• Add maven-settings-builder for plexus-sec-dispatcher 4.x tests

POM Improvements:

• Improve XML formatting and readability
• Add explanatory comments for dependency decisions
• Consolidate version properties

chore: Update GitHub Actions workflows to Java 21
chore: fix gpg private key reference for CICD

• Upgrade checkout action from v3 to v5
• Upgrade setup-java action from v3 to v5
• Upgrade setup-maven-action from v1.11.0 to v1.19.0
• Update JDK version from 8 to 21 across all workflows
• Switch maven-publish workflow to Zulu distribution for consistency

This aligns the CI/CD pipelines with the Java 21 baseline requirement
established in the project dependencies.

fix(ci): Remove duplicate GPG key import in release workflow

Remove manual GPG import step that was conflicting with setup-java's
built-in GPG handling. The duplicate import was causing exit code 2
errors during both setup and cleanup phases.

Now relies entirely on setup-java@v5's declarative gpg-private-key
and gpg-passphrase configuration for cleaner key management.

Fixes the "Failed to remove private key" error in GitHub Actions.

Full Changelog: v0.9.18...v0.9.19