unlock installer strategies

[Gankra]

There are two major strategies for installers, "fetching" and "bundling". Currently each kind of installer is hardcoded to a strategy, but it would be cool if we could make that configurable (where it makes sense):

Glossary:

• ✅ implemented
• ❔possible
• ❌ probably wouldn't make sense

	Fetching	Bundling
shell	✅	❌ (1)
powershell	✅	❌ (1)
npm	✅	❔(2)
homebrew	✅	❌ (3)
msi	❔(4)	✅

Notes:

1. shell/powershell installers that bundle binaries are a horrifying concept that should not be considered
2. npm packages that bundle binaries could make sense, I think people do it, although they use a complicated system where they have one package for each platform, and then a meta-package that depends on them all and picks the right one at install-time
3. homebrew installers cannot bundle binaries, but they can be from-source (not currently interested in exploring that space)
4. fetching msi's make perfect sense, we just defaulted to bundling as more conventional and friendly to enterprises