Add brave template command

[Szubie]

A common problem is that a user may not know where to start if asked to create a Bravefile from scratch. The syntax can be difficult to remember - often they are tempted to copy-paste existing Bravefile examples and tweak them for their current application, which isn't ideal.

The brave template command in this PR creates an example Bravefile with commonly used settings and saves it in the current working directory, giving users a place to start and removing the need to refer to pre-existing Bravefiles.

The Bravefile created looks like this:

image: example-image/v1.0

base:
  image: alpine/3.16

packages:
  manager: apk
  system:
    - curl

run: 
  - command: echo
    args:
      - hello world

copy:
  - source: ./Bravefile
    target: /root/

service:
  name: example-container
  ports:
    - 8888:8888
  resources:
    ram: 2GB
    cpu: 2