[rush] Allow global configuration of package manager settings that Rush passes during install

[D4N14L]

Is this a feature or a bug?

• Feature
• Bug

Please describe the actual behavior.

There are some settings/features that package managers provide that users may want to set every time they run an install. A good example of this would be network timeout settings, which

• vary on availability depending on the package manager used (ex. fetch-retry-factor in PNPM, or network-timeout in Yarn)
• need to be passed in every time the install/update command is run

Currently, Rush does not support passing in any package manager specific values that aren't explicitly supported on the rush install/rush update CLI, or specified in rush.json package manager options. This is limiting because

• the CLI arguments are meant to be applicable to all package managers, and having arguments that apply to one package manager but not to another is confusing
• the rush.json file is checked in, and settings that are optimal for one developer may not necessarily apply to another

What is the expected behavior?

These types of settings do not materially impact how the Rush repo may be expected to install, but instead are modifiers to improve developer experience. That's not to say some solution should/shouldn't allow changing things that materially affect install, though this is more of a slippery slope that I'm not trying to address with this issue. I'm personally of the opinion that dangerous settings like that should be tightly controlled by the repo manager (as is currently done with package manager-specific settings in rush.json).

One option would be to use a settings file (or files) in the home directory (under ~/.rush, for example) to store these settings. This file (or files) could be strongly validated against a schema, or compared against a whitelist of known parameters that could be used to warn if a provided value was not known to be supported. The values inside this file would then be passed on to the package manager whenever rush install or rush update is run.