visible indication while fetching the public node listing

[dherman]

I believe fetching the public node listing is causing a pause with no visible indication to the user. Test this hypothesis, and if it's true, we should:

• show an activity and/or progress indicator while fetching it
• possibly cache it

I'm not sure if the caching semantics works, since it could mean missing new versions. So we should think that through.

[mikrostew]

When running notion install <version> I am seeing a pause during this period, especially on my slow home internet.

A quick check shows this is taking almost 3/4 of a second for me:

$ time curl https://nodejs.org/dist/index.json
(...lots of JSON...)

real	0m0.705s

I don't think that caching makes sense for this, unless there is syntax to install multiple node versions at the same time, something like notion install 8.9 9.4.7 lts. In that case we should only fetch the public registry once.