feat: add shell type for APP instruction

[kakaZhou719]

Describe what this PR does / why we need it

sometimes when installing an app type cluster image, we need to configure some additional information. such as some k8s cluster resources which cannot be directly written in the yaml file as fixed value.

if so, we nee add shell type for APP instruction, and it does not affect the current usage.

for shell :

1. if local file is normal file and the suffix of this file ends with a ".sh", will copy it to rootfs ,and write its launch cmd in sealer image extension at build stage.
2. if local file is dir, will walk though the target dir , and collect all files which suffix is ends with a ".sh", then write its launch cmd in sealer image extension at build stage.

below is my test kubefile:

FROM scratch
APP config local://config.sh
APP my-shell local://shell 
APP dashboard local://dashboard.yaml
LAUNCH ["config","my-shell","dashboard"]

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