Add "@asset" to decorate a function as a DAG and an asset

[uranusjr]

Why

As part of AIP-75

What

Add an asset decorator which can be used to decorate a function and create a DAG and an asset.

@asset(uri="s3://bucket/object", schedule=None)
def asset2_producer(self, context, asset1_producer):
    print(self)
    print(context["inlet_events"][asset1_producer])

In the example above, it create a DAG(dag_id="asset2_producer", schedule=None, ...) and an Asset(name="asset2_producer", uri="s3://bucket/object"). Inside the function, self can be used to access the asset with name asset2_producer, context is just like context in a normal task and asset1_producer is used to access an asset with name=asset1_producer

Closes: #42314

[github-actions]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed in 5 days if no further activity occurs. Thank you for your contributions.

[Lee-W]

@uranusjr I tried to make the @asset work and added an example DAG and some unit tests. The next thing I will work on is accessing self and context. But would be great if you could take a look in advance in case I'm doing something wrong. Thanks!

[uranusjr]

GitHub seems to have changed something and now I can’t approve my own PR. So consider this as a manual approval. ✅

[Lee-W]

GitHub seems to have changed something and now I can’t approve my own PR. So consider this as a manual approval. ✅

Thanks! Let me merge it now

[potiuk]

GitHub seems to have changed something and now I can’t approve my own PR. So consider this as a manual approval. ✅

They are really experimenting with Approvals it seems......