feat(sites-create-template): auto-link cloned repo to the created net…

[benhancock]

…lify site

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Summary

Fixes #4438

This PR adds functionality (requested in #4438) to sites:create-template wherein after cloning the newly created repo, the cli will prompt the user asking if they'd like to link the directory to the cloned repo.

This is what the user saw before our changes:

This is the dialog the user sees with our changes:

This PR also contains tests for the new functionality and error handling, including in the case of a site already being linked to a parent directory.

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