Modernization updates

[mswatosh]

This PR has a number of updates to modernize the spec to current Jakarta/Maven/Github best practices.

Updating sig-test to Jakarta EE standard method

• Replaced the old asignature test setup with the Jakarta EE standard approach using jakarta.tck:sigtest-maven-plugin v2.3.
• Added a signature-generation profile to tck/pom.xml that unpacks the API jar, generates a .sig file named by JDK major version (e.g. jakarta.json.sig_17), and copies it to the test resources.
• Added a tck-tests-ci profile to tck/tck-tests/pom.xml that runs all TCK tests (including sig tests) against Eclipse Parsson as the compatible implementation.
• Switched to java version based tagging for the signature files e.g. jakarta.json.sig_17
• Bumped the Parsson compatible implementation reference from 1.1.0 → 1.1.8

Modernizing poms

• Bumped the org.eclipse.ee4j:project parent POM to 1.0.9 across api/pom.xml, spec/pom.xml, and tck/pom.xml.
• Upgraded multiple Maven plugin versions (maven-compiler-plugin, maven-jar-plugin, maven-javadoc-plugin, maven-enforcer-plugin, build-helper-maven-plugin, spec-version-maven-plugin, maven-assembly-plugin).
• Replaced maven.compiler.source/target with maven.compiler.release=17 in the TCK POM.
• Upgraded JUnit Jupiter from 5.7.2 to 5.14.4 and switched to importing the junit-bom for dependency management.
• Added flatten-maven-plugin (1.6.0) to api/pom.xml for POM flattening.
• Re-enabled the check-module goal in spec-version-maven-plugin (previously commented out with a TODO).

Updating actions build and adding dependabot

• Added .github/dependabot.yml to enable automated daily dependency updates for both Maven and GitHub Actions.
• Updated the CI workflow to add Java 25 to the test matrix, pinned actions/checkout to v4.2.2 and actions/setup-java to v5.6.0 by commit SHA
• Switched the JDK distribution from zulu to temurin.