Helpers and keywords unification

[m-wcislo]

@Nilsty, @satish-nubolab, @mika-b - I'm planning to cleanup the keywords and helpers a little bit to make whole thing more DRY, clean etc. The idea is to make all the keywords always return k8s objects not their names in some cases. To get names or anything more specific we should use helpers (filters).

The old functions will be marked deprecated and kept till v1.0.0. Let me know your thoughts (also keyword naming convention proposal are welcome). Currently the PR has minimal POC version to show how it would look like and what are the efforts.

Before merge following needs to be applied:

• At least one example testcase added in testcases/
• Library Documentation regenerated according to Generate docs
• All new testcases tagged as prerelease along other tags to exclude it from execution until released on PyPI
• Coverage threshold increased in .coveragerc if new coverage is higher than actual, see the lint-and-coverage step in CI

fail_under = 67

[Nilsty]

I like the idea of always returning the full k8s object or list of objects for the mail keywords. When using the KubeLibrary I personally don't use any of the filter keywords and rather filter the k8s object myself in custom keywords. From my point of view the filter keywords are not needed. Having good test cases examples to build custom filters works better for me.

My naming proposal would be to keep it close to the kubernetes api function names. e.g. Get Services In Namespace should be List Namespaced Services and Get Service Details In Namespace should be Read Namespaced Service.

[Nilsty]

@m-wcislo The changes look good. Good job. I really like the new filter keywords e.g. filter_names and filter_by_key.

[m-wcislo]

@Nilsty docs generted and release prepared, please approve.

[Nilsty]

LGTM