feat: pass forceCloseConnections option from cli

[LucaRainone]

Enabling the proxy for the forceCloseConnections option. When enabled, this option resolves this issue. Explained in detail also inside this other issue

Please note that the original option on fastify could be both string and boolean. In fastify-cli I didn't find a smart way to manage it (it seems that's possible defining only one type in a structural way). I choose to use it as boolean/flag, leaving the only allowed string value (idle) the default option. If there is a better standard solution, please point me in the right direction :)

Checklist

• [x] run npm run test and npm run benchmark
• [x] tests and/or benchmarks are included
• [x] documentation is changed or added
• [x] commit message and code follows the Developer's Certification of Origin and the Code of conduct