feat: stop vm when agent finished executing

[MurielParaire]

What does this PR do ?

It sends a request to the agent to stop after they have finished executing the code

How to test ?

You need to open 3 command lines simultaneously and launch these three commands:

Api:

cargo run --bin api

Vmm

cargo build
sudo -E capsh --keep=1 --user=$USER --inh=cap_net_admin --addamb=cap_net_admin -- -c  'RUST_BACKTRACE=1 '$CARGO_PATH' run --bin vmm -- grpc'

Client:

cargo run --bin cli run --config-path <path_to_cloudlet>/src/cli/config/config.yaml

You should see a vm booted on the vmm terminal that launches the agent and stops as soon as the code is finished executing

[mfernd]

By default, the Default implementation is ServerConfig { address: "", port: 0 }.

It would be better to implement it ourselves, so impl Default for ServerConfig { ... } with localhost and 50051 for default values.

[mfernd]

Should the VMM be started by the API instead of manually? (since we are shutting it down when the execution is finished)

Note: closing it, and will consider it in another iteration