Upgrade plugin to Grails 6.x

[vsachinv]

@sheehan I have upgraded the plugin to Grails 6.x and also included changes requested by @kdybicz. I will publish the same to public maven repo as well.

[vsachinv]

@sbglasius Could you please check PR and let me know if I need to raise PR on https://github.com/gpc/grails-console ?

[sbglasius]

@vsachinv With the different grails versions it's hard to compare changes, but if it works on your machine, and if @sheehan accepts this PR or decides to abandon the original repo, I suggest you make the PR against https://github.com/gpc/grails-console

/Søren

[vsachinv]

@sbglasius Yes tested and working fine. Waiting for @sheehan approval.

[sheehan]

Hi @vsachinv, thank you for doing this update! One question, is it necessary to copy the plugin for each version? Originally I had separated grails2 and grails3 because they had significant changes including how the plugins were published. I haven't worked with grails for a bit and am not familiar with whats changed in the last few versions, but I assume we'd just want to publish one new version in Maven Central that would be compatible for grails 3-6? Is that correct?

[vsachinv]

@sheehan No not required but UI generate scripts were written for Grails specific versions so rather altogether removing and revamping whole code base I followed the same pattern having folder for each version. I would clean up if required.

[sheehan]

I'm archiving this repo as suggested by @sbglasius so I guess you should move this PR to the gpc repo.