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**:
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