Support FeatureView as DataSource

[HaoXuAI]

Is your feature request related to a problem? Please describe. A clear and concise description of what the problem is. Ex. I'm always frustrated when [...]

Since the DAG was introduced in the compute engine, the data source can now be a feature view.

Describe the solution you'd like A clear and concise description of what you want to happen. Example:

bfv1 = BatchFeatureView(
source=FileSource(...)
)
bfv2 = BatchFeatureView(
source=bfv1,
...
)

Can start as single feature view as source, and expand to multiple data sources + feature views as source.

Describe alternatives you've considered A clear and concise description of any alternative solutions or features you've considered.

Additional context Add any other context or screenshots about the feature request here.

[HaoXuAI]

WIP