[question] Documentation for `core.download:download_cache`

### What is your question?

The `core.download:download_cache` config is mentioned in https://docs.conan.io/2/reference/config_files/global_conf.html but not really described anywhere. Would it be possible to provide some more information for this feature?

My understanding is that it can be used on a CI node to prevent the need to repeatedly download dependencies from a Conan remote every time a job is run. Is it suitable for this use case?

More specifically, are there concurrency guarantees? For example, is safe to use even if multiple executors are running simultaneously on the same machine?

Finally (unrelated to this) what is the best way of programatically applying a `core.*` config value? Conan v1 had `conan config set`. It looks like `core` config can't be overridden with profiles or commandline parameters. Does this mean the only way is something like `echo "core.foo=bar" >> .conan2/global.conf`, or is there a better way?

Many thanks for your help.

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