feat(@angular/cli): implement --registry for ng add

[tiaguinho]

This PR close #14189

[dherges]

Hi @tiaguinho,

thanks for sharing your time to implement this! I am looking forward to the next release.

[blemaire]

Hi all, which version is this going to be in? I was hoping to use it but 7.3.9 does not have it 😢

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