feat(@angular-devkit/schematics-cli): auto detect package manager

[MarvinXu]

PR Checklist

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PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• Other... Please describe:

What is the current behavior?

Can't specify packageManager when running a schematic

Issue Number: N/A

What is the new behavior?

Detect packageManager by the lock file, and use the right package manager to install dependencies. Behave like ng generate <schematic>

Does this PR introduce a breaking change?

• Yes
• No

Other information

This PR originates from nestjs/nest-cli#1115

As I look into the problem, first I wanted to fix it in @nestjs/schematics

but then I checked Angular cli, and run the following command, it worked as excepted(using correct package manager).

ng new test --no-install
cd test
touch yarn.lock
ng g @nestjs/schematics:resource --name=users --no-dry-run --no-skip-import --language="ts" --source-root="src" --spec --no-flat

So I thought maybe it's better to fix it in schematics-cli to make it behave just like angular-cli.

I am a new contributor, plz let me know If I did anything wrong ;)

[clydin]

Thank you for the contribution.

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