Lower dependency version, delete package-lock.json, use Fastly build action for CI

[harmony7]

This PR lowers the dependency version of @fastly/js-compute to ^3.0.0 and removes package-lock.json (or npm-shrinkwrap.json).

In a starter kit, we should declare a version of the SDK that has the features needed (^3 in this case), as well as dependencies. And by not including package-lock.json, the user always gets the newest compatible version at the time their project is initialized, and a new lock file that they would commit to their new project's code repo.

For example a new user kicking off with this starter kit today would get 3.8.3 because that matches ^3.0.0. A person who runs this starter kit next week might get 3.9.0 if that is available by then, and so on.

[harmony7]

I've added updates to the CI build:

• Use npm install instead of npm ci - this now necessary as a result of this PR
• 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@3af2ae5