Manually execute `ng new` deps postinstall scripts

# 🚀 Feature request

### Command (mark with an `x`)

- [X] new

### Description

Currently, `ng new` will automatically run `npm install` which (if the user has not disabled it), automatically runs all postinstall scripts. This can be a vulnerability since any compromised package in the NPM dependency graph could add a postinstall step to install malware on developer machines.

### Describe the solution you'd like

We could reduce the attack surface by disabling postinstall on the automatic `npm install` and then manually invoke the postinstall for a known set of required packages. Only 3 packages currently use postinstall steps, so limiting execution to just those would significantly reduce the attack surface for a potential supply chain attack.

One possible concern is for dependencies which add a required postinstall step in the future. We can pretty easily add a test to make sure we aren't missing any postinstall steps from our transitive dependencies, though this inherently breaks abstraction somewhat. Adding a postinstall step is (somewhat debate-ably) a breaking change, so any package which adds one in the future should require a major version bump where we have an opportunity to allowlist it.

The one edge case I can think of is if we have:

```
ng-new-app@0.0.0 -> package-a@^1.0.0 -> package-b@^1.0.0
```

And `package-b` gets a new postinstall step in `v2.0.0`. However, `package-a` may be able to manage the breakage without violating their own public API (or maybe doesn't notice the new postinstall step) and simply bumps to `v1.0.1`. This would immediately be pulled in to the next `ng new` command and fail. I think such a scenario would actually be a bad patch release for `package-a`, since adding a required postinstall step is fundamentally a breaking change. We would rely on NPM package maintainers to make the right semver-compatible decisions for a somewhat nuanced case, but this is probably better than the alternative.

Start by examining the ng new flow that automatically runs npm install and determine how postinstall scripts are currently handled. Done means disabling the broad automatic postinstall execution, invoking only the required known packages, and adding coverage to detect missing postinstall dependencies.

Written by the indexing model from the issue text.