Update plugins

[holgerfriedrich]

Update nearly all plugins listed by mvn versions:display-plugin-updates -nsu -B -Dversions.outputLineWidth=120 | grep -- '->' | sort -u (except the ones related to Karaf 4.4.6 update and milestone/snapshot releases, openapi-generator, jaxb2 (as this one has another provider as in core, tbc))

• set minimum Maven version to 3.6.3
• build-helper-maven-plugin, 3.4.0 to 3.5.0, see https://github.com/mojohaus/build-helper-maven-plugin/releases/tag/3.5.0
• frontend-maven-plugin, 1.13.4 to 1.15.0, see https://github.com/eirslett/frontend-maven-plugin/blob/master/CHANGELOG.md
• license-maven-plugin, 4.2 to 4.3
• maven-clean-plugin, 3.3.1 to 3.3.2, see https://github.com/apache/maven-clean-plugin/releases
• maven-dependency-plugin, 3.6.0 to 3.6.1, see https://github.com/apache/maven-dependency-plugin/releases/tag/maven-dependency-plugin-3.6.1
• maven-enforcer-plugin, 3.4.0 to 3.4.1
• maven-jar-plugin, 3.3.0 to 3.4.1, see https://github.com/apache/maven-jar-plugin/releases
• maven-javadoc-plugin, 3.2.0 to 3.6.3, see https://github.com/apache/maven-javadoc-plugin/releases
• maven-plugin-plugin, 3.9.0 to 3.12.0, see https://github.com/apache/maven-plugin-tools/releases/tag/maven-plugin-tools-3.12.0
• maven-site-plugin, 3.12.1 to 4.0.0-M13
• maven-source-plugin, 3.3.0 to 3.3.1
• maven-surefire-plugin, 3.1.2 to 3.2.5, see https://github.com/apache/maven-surefire/releases
• sortpom-maven-plugin, 3.3.0 to 3.4.1
• spotless-maven-plugin, 2.38.0 to 2.43.0, see https://github.com/diffplug/spotless/blob/main/plugin-maven/CHANGES.md