Add ability for pre-start script

[M1kep]

This is a proposal to add the ability for users to further extend the image with their own custom startup scripts.

The startup script should be created by the user at ./storage/scripts/pre-start.sh

My particular use case is to install some additional python packages for debugging, without needing to rebuild the whole image locally(Which for some reason fails.. but I haven't looked too deeply into that.)

[YanWenKun]

Merged! Note that entrypoint.sh has set -e, it will stop if pre-start.sh run into error. You can override that like:

# pre-start.sh
set +e
chmod +x another-script.sh
bash another-script.sh

# another-script.sh
set -e
step1
step2
...

So the another-script.sh will stop if any step returns error. But pre-start.sh will just skip that and continue starting ComfyUI.