feat: add install script for the GraphQL CLI

[jlengstorf]

IMPORTANT: We can't merge this until (unless?) https://github.com/graphql-cli/graphql-cli/pull/79 is merged in.

This adds an install script that will:

• Update package.json with a new name and description
• Prompt the user for a prefix and namespace
• Replace the placeholder strings with user-supplied values

Current issues:

• [x] The CLI should ignore install.js

[jlengstorf]

Here's a screenshot of the install prompts + the diff after it runs:

[kbrandwijk]

The PR on graphql-cli is merged! 🎉

[jlengstorf]

CLI ignores the install script now: https://github.com/gramps-graphql/gramps-cli/pull/31