Allow config overrides e.g. npmrc for built ins

We need to allow users to override specific configurations for runtimes and tools. For example, in an ADO context, the azure devops MCP should only install from internally managed feeds. Teams usually have an npmrc to configure this.

Likewise, a similar runtime for node will have the same need to pull and build only from internally managed feeds.

Different languages have different configurations, but they mostly boil down to a set of url endpoints in a file. The file needs to usually be injected into any commands that would install from a feed, and urls contained in the feed config file would need to be allow listed in the firewall.

Some runtimes pick up configuration automatically, like cargo. Which picks up config.toml from a well understood location (.cargo if I remember correctly). We need to come up with a plan that encompasses all these use cases.