Configure Dependabot for npm packages at the template level

[browniebroke]

Description

Changes to get Dependanbot updates for npm packages:

• Update Dependabot config
• Remove all the Jinja tags from the package.json in order to make it parsable by Dependanbot
• Remove unwanted dependencies in post-generation hook, to replace what was done by templating

Checklist:

• I've made sure that tests/test_cookiecutter_generation.py is updated accordingly (especially if adding or updating a template option)
• I've updated the documentation or confirm that my change doesn't require any updates

Rationale

We can't keep npm packages up to date because they are not automatically updated.

[browniebroke]

Let's give this one a try.