New generic API client for less code duplication

[LittleFox94]

Description

This PR adds a new generic API client only requiring a handful lines of code on an API resource to be compatible to it. It's inspired by the kubernetes client, but not completely following it.

Many people reviewing this would be appreciated, while it seems to work with the already implemented API resources, I'm not sure if it's generic enough for all our APIs.

Feedback on the usage interface of this new client is also appreciated, I have uploaded the docs for this branch to the webserver to my home router (it's a wget -nH -m $godoc_server and some nginx redirects).

Release Note

Release note for CHANGELOG:

* adding a new generic API client, hopefully leading to way less code duplication in this package. The existing interfaces are still fully supported and not (yet, might happen in the future) deprecated.

References

• Add Pagination to LB API #45 (comment)

Community Note

• Please vote on this issue by adding a 👍 reaction to the original issue to help the community and maintainers prioritize this request
• If you are interested in working on this issue or have submitted a pull request, please leave a comment

[LittleFox94]

Mirroring comment from @toothstone in internal ticket:

It might be a good idea to then upgrade one of the more challenging packages (e.g. vsphere) first, to really test out the limits and adapt where necessary.

This might even be still in scope of this PR

[kstiehl]

Haven't looked at the pagination package yet

But here are some of my findings
In general i like the refactoring just a few things

also please adjust all errors so that they are not capitalized anymore.

[LittleFox94]

I think I addressed all your review comments and fixed them in one way or another.

I also implemented filters on listing LBaaS backends as example (and for my tests). Oh right, I made all the examples to working, runnable tests - 73.5% coverage from only the examples already :)
Will add more tests, but another review already would be appreciated.

[kstiehl]

Sure will have another look

[codecov-commenter]

Codecov Report

Merging #56 (aacb872) into main (815fcca) will increase coverage by 8.48%.
The diff coverage is 93.89%.

@@            Coverage Diff             @@
##             main      #56      +/-   ##
==========================================
+ Coverage   45.40%   53.88%   +8.48%     
==========================================
  Files          76       82       +6     
  Lines        2938     3511     +573     
==========================================
+ Hits         1334     1892     +558     
- Misses       1271     1286      +15     
  Partials      333      333              

Flag	Coverage Δ
integration	45.13% <0.00%> (-1.10%)	⬇️
unittests	20.79% <93.89%> (+14.93%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
pkg/lbaas/frontend/api.go	13.33% <0.00%> (-86.67%)	⬇️
pkg/lbaas/loadbalancer/api.go	35.71% <25.00%> (-64.29%)	⬇️
pkg/lbaas/backend/api.go	89.28% <88.46%> (-10.72%)	⬇️
pkg/api/api_implementation.go	96.46% <96.46%> (ø)
pkg/api/errors.go	100.00% <100.00%> (ø)
pkg/api/internal/options.go	100.00% <100.00%> (ø)
pkg/api/options.go	100.00% <100.00%> (ø)
pkg/api/pagination.go	100.00% <100.00%> (ø)
pkg/api/types/options.go	100.00% <100.00%> (ø)
pkg/client/log_utils.go	89.15% <0.00%> (+8.43%)	⬆️
... and 1 more

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