Updates to plugin

[cstamas]

Changes:

• add dependabot to GH actions as well
• make CI run matrix on Maven to ensure it works (as prerequisite only prevents execution) and use mnvw. In general do NOT rely on Maven brought by setup-java, only as "bootstrap" Maven, control actual versions using Wrapper.
• update Maven Wrapper to latest and use type "only script" (it is best and newest, as it merely delegates to real mvn script)
• Update some plugins
• update some configs to stop warnings about config deprecation
• detach plugin "prerequisite" and "dependency", use prerequisite as wanted (3.2.5) but build against latest (3.9.6)

Rationale of that last one is:

• be up to date regarding deprecations, recent changes in Maven Core
• but run the build/ITs with full range of supported Maven versions, and that will catch for sure any incompatibility

[cstamas]

One recommendation: prerequisite Maven version 3.2.5 is really old (10 years!). ASF Maven Core plugins are moving to prerequisite of 3.6.3, FYI.

[gaul]

Thank you for your contribution @cstamas!