Use Fastly compute action for CI build

[harmony7]

This PR updates the CI build:

• Use npm install instead of npm ci - this now necessary as a result of Lower dependency version and delete package-lock.json #9
• Use Fastly actions to install the CLI and run the build, rather than the previous strategy of directly calling js-compute-runtime.

This is based off of @kpfleming 's work in fastly/compute-starter-kit-typescript-default@3af2ae5