Look for SF_NPM_REGISTRY

[iowillhoit]

What does this PR do?

We suggest using SF_NPM_REGISTRY

Deprecated environment variable: SFDX_NPM_REGISTRY. Please use SF_NPM_REGISTRY instead.

However, plugin-trust did not look for that env var when verifying signatures.

QA

You can link this to your locally installed sf. After linking and setting a bogus registry with SF_NPM_REGISTRY, you will see a warning

{
  errno: -3008,
  code: 'ENOTFOUND',
  syscall: 'getaddrinfo',
  hostname: 'registry.npmjs-foo.org'
},

What issues does this PR fix or reference?

forcedotcom/cli#2517
@W-14277809@

[WillieRuemmele]

QA Notes

---

before:

setting the env had no effect

 ➜  SF_NPM_REGISTRY=abc.com sf plugins install @salesforce/plugin-packaging
Polling for new version(s) to become available on npm... done
Successfully validated digital signature for @salesforce/plugin-packaging.
Finished digital signature check.

after:
✅ : the env is respected

 ➜  SF_NPM_REGISTRY=abc.com sf plugins install @salesforce/plugin-packaging
    TypeError: Invalid URL
    Code: ERR_INVALID_URL

✅ : preferes SF_ over SFDX_ and prints a warning

 ➜  SF_NPM_REGISTRY=abc.com SFDX_NPM_REGISTRY=https://www.npmjs.com/ sf plugins install @salesforce/plugin-packaging
(node:46246) Warning: Deprecated environment variable: SFDX_NPM_REGISTRY. Please use SF_NPM_REGISTRY instead.

Your environment has both variables populated, and with different values. The value from SF_NPM_REGISTRY will be used.
(Use `node --trace-warnings ...` to show where the warning was created)
    TypeError: Invalid URL
    Code: ERR_INVALID_URL