[TASK] Initialize existing repos with the CLI

[Serial-ATA]

Might be worth allowing the following:

• You clone a template, say https://github.com/tangle-network/blueprint-template
• You can initialize it in place: cargo tangle blueprint create --name foo --init
• cargo-generate.toml is deleted and all placeholders are updated

Don't know if this is possible with cargo-generate, just a thought.