CI: Re-enable Windows for testing

[SchoolGuy]

Fixes #2

The scope of this PR was expanded due to details that appeared during the actual bugfix. This PR now contains changes for the following things:

• CI: Enable Windows for testing
• CI: Only send coverage to Codacy when running on Linux
• Tests: Replace https://github.com/ContainerSolutions/go-utils with our own code
• Tests: Add support for multi-buffered requests and responses
• Items: enable_gpxe was renamed to enable_ipxe
• Client: Add helper method IsValueInherit
• Tests: Remove mock system creation and use the real method

The code in this PR was not validated against a running Cobbler instance.

[SchoolGuy]

It appears that we are running into golang/go#51269

[SchoolGuy]

After a bit of investigation, it appears that we are using the StubHTTPClient which is coming from http://github.com/ContainerSolutions/go-utils. This is a problem as the comparison that lets the Windows CI fail is done in that package.

[SchoolGuy]

I will extend the scope of this PR to also remove go-utils from the dependencies of the project so we can have our own implementation of an HTTPClient. This allows us then to use buffered responses for multiple requests and responses per-test.

[SchoolGuy]

Working on this PR showed that the creation of objects is not possible since we are using the embedded item structs due to the method updateCobblerFields not being able to handle that.

[SchoolGuy]

Okay Windows likes use now. Let's get back to fixing the skipped tests.

[codacy-production]

Coverage summary from Codacy

See diff coverage on Codacy

Coverage variation	Diff coverage
✅ +4.20% (target: -1.00%)	✅ 66.99%

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (caa2583)	2111	993	47.04%
Head commit (0ff47d4)	2258 (+147)	1157 (+164)	51.24% (+4.20%)

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#31)	103	69	66.99%

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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[tiltingpenguin]

I just have some minor things I want to clarify, otherwise LGTM. One general comment I want to make though is that the DeleteItemRecursive tests seem kind of useless to me since we only test them in the false case where the behaviour is the same as in the non recurisve function