upgrades/refactoring

[silannisik]

Hi,

We've been using this repository for onboarding new teams on DSH.
The changes we made to the repo are included in this PR.

• Updated Docker plugin to fabric8io and specifying the platform as linux/amd64, otherwise the container doesn't work when building on M1 chips and running it in a tenant
• Added an example folder with a script to subscribe and publish using MQTT with reference to the DSH documentation and example output
• Upgraded Java version (8->17)
• Refactored code, put classes into separate packages, removed unused imports, fixed typos
• Pass uid:gid as build arguments in Dockerfile, so we don't need to change the source when using it in different tenants

[rutgerc-klarrio]

I would keep the uppercase ARG names. I believe in docker files it is the more popular style.

[rutgerc-klarrio]

I understand that it is example code, but it might still be worth it to look at using a logging library iso using print statements.

[gert-verbruggen-klarrio]

See the remarks of Rutger about the uppercase IMAGE_VERSION and the logger.