[GOCA] add state values and strings for the host

[treywelsh]

Description
In the file host.go from the go bindings, there is no values and associated strings for the State of the host.
It's done for other elements, see other files image.go or vm.go.
Theses values are documented in the XMLRPC API documentation.

Use case
I should be more easy to develop tools with it.

Interface Changes
It will not change the existing interface, it's about adding an enum of values an associated String method.

Additional Context
I will create a pull request with my suggestion

Progress Status

• Branch created
• Code committed to development branch
• Testing - QA
• Documentation
• Release notes - resolved issues, compatibility, known issues
• Code committed to upstream release/hotfix branches
• Documentation committed to upstream release/hotfix branches