feat(init): add new config to `npm init` for setting `private` value (ie. `--init-private`)

[darcyclarke]

[wraithgar]

npm init does not currently have a config item that alters the private flag.

[ljharb]

When this was filed, the intention was to ship in npm 8 a config item for this that defaulted to false.

[lukekarrys]

I have the same recollection as @ljharb and think this should be changed to add a config option for this. Obviously that makes it no longer a breaking change.

[ljharb]

Is it too late to semver minor it into v8?