Move namespace mapping to `~/.config/warg/config.json`

[lann]

It currently goes in ~/.cache/warg/namespaces, which seems wrong for this kind of configuration.

[calvinrp]

Currently, there isn't a user config option to set a namespace mapping to a registry domain. This namespace mapping is only for hint header accepted mappings and operator log import namespace mappings.

When you do warg reset or change your home registry (which does a warg reset), the namespace mappings are removed.

So it probably makes sense in the current cache path along side the package log cache, given the behavior.

When we add user configurable namespace mappings, they should be part of the config, as you are suggesting here.