Add hostgroup edit feature

[hsorellana]

This PR adds the ability to edit (for now) the display_name field for a HostGroup resource without having to recreate any dependent resource. Plus, it adds a second TestStep which acts as an update scenario. Comments are welcomed!

[hsorellana]

The build fails due to version mismatch: i have go 1.13 and the build uses 1.11. I don't want to just go ahead and change the build version without checking with you first, so what should we do here?? @paultyng

[paultyng]

@hsorellana sorry, in the middle of transferring this repo, hopefully the maintainers can respond once we complete the transfer process, I'm not familiar with its inner workings, just tasked with the transfer process.

[attachmentgenie]

in the mean time this repo has moved into the icinga org, and we are happy to bump the go version we build with, i even bumped it to 1.14. @hsorellana can you try building again?

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