Update dependencies + CI

[harmony7]

This PR:

• Removes package-lock.json (as is being done in other starter kits)
• Adds post_init script to run npm install after "fastly compute init" (as is being done in other starter kits)
• Updates TypeScript to ^5
• Removes expressly (it wasn't being used in this starter kit)
• Removes Webpack (not necessary for this starter kit)
• Adds the CI build (as in other starter kits)