Add --cache-file flag to `render` command

I'm using skaffold render in my CI/CD GitOps pipeline, and would like to reuse Skaffold cache file between runs, to avoid the dreaded Checking cache... Not found. Building. However, I need to write this cache file to a specific location that's not $HOME/.skaffold/cache, because that directory is not preserved between my CI steps.

I could move the directory explicitly before/after running skaffold render, but it's pretty inconvenient. Other commands (build, dev etc.) expose --cache-file flag to specify its location, and I'd like it to be added to render as well, if possible.

Alternatively, if there's any way to set the "Skaffold directory" (from the default $HOME/.skaffold), that could work too (and maybe even better!)

Expected behavior

skaffold render has --cache-file flag

Actual behavior

--cache-file flag is not available for skaffold render

Information

• Skaffold version: v1.34.0
• Operating system: Ubuntu 20.10
• Installed via: Cloud Code
• Contents of skaffold.yaml: N/A

Steps to reproduce the behavior

1. Run skaffold render --cache-file=.skaffold/cache
2. Observe the result:

unknown flag: --cache-file
See 'skaffold render --help' for usage.