✨ [Docker] Further Docker images footprints improvements

[Coduz]

This PR amis to further improve Docker images optimisation to reduce footprint of the images.

Optimisations have the following results

Container	Before	After
kapua/java-base	591 MB	545 MB
kapua/jetty-base	639 MB	573 MB
kapua/kapua-sql	595 MB	549 MB
kapua/kapua-events-broker	848MB	802 MB
kapua/kapua-api	905MB	838 MB
kapua/kapua-job-engine	873MB	806 MB
kapua/kapua-broker-artemis	943MB	897 MB
kapua/kapua-service-authentication	716MB	670 MB
kapua/kapua-consumer-lifecycle	730MB	684 MB
kapua/kapua-consumer-telemetry	721MB	675 MB

The java-base image shrinks of 46 MB, which are saved for each of the Docker container that are using it (all of them).

Related Issue
None

Description of the solution adopted
Optimization performed:

1. run microdnf clean all to remove all microdnf packages metadata
2. removed /opt/jetty/demo-base directory, not needed in our jetty-base image

Screenshots
None

Any side note on the changes made
None