[Feature] Give a mechanism to leave workload alive when it's component not used in AppConfig

[wonderflow]

A Component could be some kinds of resource like Database or Storage system. Once an app not need this component, it may be deleted from AppConfig but the resource should keep alive for a period of time for security or other needs.

[BBialeckiACR]

I believe this is exactly why my concept of entrypoints needs to be implemented. Then these can be specified in separate app configs and referred to as component entrypoints in another.
But we had also thought of this as something that could be specified in a custom trait.

[wonderflow]

@BBialeckiACR Yes， a custom trait is much better as we don't need to add any concepts to current OAM spec.

[BBialeckiACR]

The issue with a custom trait is that there can be no default value define by a developer and this is left in the hands of the implementation

[resouer]

@BBialeckiACR I'm thinking maybe it's possible to define default values in TraitDefinition (as we already did in kubevela's implementation).