feat(repo): add command to create bundle

[echocrow]

bootstrap a new bundle file, ideally with a template providing various hook function, e.g.

#!/bin/bash
#
# My custom Tildepot bundle

function SKIP() {
  # Check if the entire bundle should be skipped, e.g.
  # [[ $(hostname -s) == 'MyOtherDevice' ]] && echo 'Skipping on my other device'
}

function INSTALL_SKIP() {
  # Check if install should be skipped, e.g.
  # [[ tilde::cmd_exists my_cmd ]] && echo "Already installed"
}
function INSTALL() {
  # Optional install steps
}


function UPDATE() {
  # Optional update steps
}

# ...

additionally, the command could prompt for a parent bundle to extend. in that case, maybe the bootstrapped user bundle file is drastically simplified (i.e. just file shebang, file description, and export INHERIT). in a later iteration (#12), bundles could define or generate a customized bootstrap user bundle file