toolchain slimming options

[softprops]

Describe the problem you are trying to solve

Describe the solution you'd like

I'd like a way to opt out of any default component that isn't essential for build and test to install the smallest possible toolchain.

I believe rustup installs more than that including vendored copies of multiple books and other documentation with no way to opt out

Notes

I have docker containers that install rust with rustup for cases solely targeting building and testing. I would like these build containers to be as small as possible.

[kinnison]

This kind of functionality is that intended by the profiles concept being developed by @nrc.

[lnicola]

Duplicate of #998.

[softprops]

@lnicola I subscribed to the other issue which has more momentum and commentary. I'll close this in favor of that