Automatic merge from submit-queue
go-client: Use httpcache client for all requests, even though only openapi returns ETags for caching
**What this PR does / why we need it**: Use HTTP ETag for caching Swagger spec download
This also adds a new command-line flag "cachedir" to specify where the cache should keep its file. It defaults to `$HOME/.kube/http-cache`.
**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: partly #38637
**Special notes for your reviewer**:
Because this adds a bunch of dependencies, and removes a couple of files, I do recommend reading each commit individually.
**Release note**:
```release-note
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Kubernetes-commit: fc89743dca6b563063b74728c3b28100cf674d9d
265b663b44