Inject values into extracted Template files

[lukeed]

Admittedly a bit of a rough approach, but it sets the stage for proper author-driven experience later on (probably 2.1)

• Chose the most popular syntax, as voted in Inject Values during Template extraction #353

• Right now, only replaces the {{ name }} string

  • Ideally, author prompts' key-names are added to the list

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Closes #353

[reznord]

that commit message tho 😆