[JS] Improve executable download troubleshooting in `@sentry/cli`

[lobsterkatie]

Problem:

The post-install script in @sentry/cli, which attempts to download the version of the sentry-cli executable appropriate to the current platform, can error out for any number of reasons, and we don't give users a lot of help when it does.

Possible solutions:

• In error message, point users to the Node installation instructions at https://github.com/getsentry/sentry-cli#node
• Improve those installation instructions to explain how people are supposed to know what to call the binary if they're using the custom CDN option. (We say The downloader will append "/<version>/sentry-cli-<dist>", but don't tell people how to determine version and dist.) Also potentially mention SENTRYCLI_USE_LOCAL.

[kamilogorek]

Improve those installation instructions to explain how people are supposed to know what to call the binary if they're using the custom CDN option. (We say The downloader will append "//sentry-cli-", but don't tell people how to determine version and dist.)

We already print a full url, including version and dist that they tried to install 🤔

sentry-cli/scripts/install.js

Line 234 in a08246d

let errorMsg = `Unable to download sentry-cli binary from ${downloadUrl}.\nError message: ${error.message}`;

I already attempted to fix this exact issue here - #833
If anyone has an idea how to improve that, I'm all for it.

[lobsterkatie]

Yup, I've seen the error message, but that tells them the name they should use in that particular instance. I was thinking something more along the lines of #1350. (I ended up halfway doing it in the process of trying to explain what I meant in this comment, so I just went ahead and finished.)

UPDATE: Of course, the moment I hit send on this comment, I realized it's more complicated than I was making it out to be, because the CDN has to host the zip, not the finished binary, and there might be a mismatch between OS/architecture on the CDN machine and the target machine. I'll move that to draft for the moment, but at least it gives you a sense what I was talking about.