[FEATURES] Option to run fuse sidecar as a init container in serverless mode

[lizzzcai]

What feature you'd like to add:

1. option to run fuse sidecar as init container in serverless mode (an annotation/label maybe)
2. fuse init container able to simple commands to perform a simple task. (for example: Copy data from cache layers to a shared volume with the main container)

Why is this feature needed:

Fuse sidecar lifecycle

For model training use case with serverless mode, the training job will keep reading the data from the data acceleration layer. In this case, the fuse sidecar will run with the main container until the job is finished. However, there are use cases that the application only needs to read/copy the data from the data acceleration layer to its local volume during the start-up time, after that the application will not interact with the acceleration layer. In this case, the fuse sidecar should work like an init container, and it is able to run business logic in a script (for example copy data to a shared volume with the main container) and then exists. Most of the fuse sidecar image is quite big and takes some resources, exists when finishing its job is able to reduce resource usage as well.