DVC: import datachain shortcut

[dmpetrov]

See this repository as an example: https://github.com/shcheklein/example-datachain-dvc

in dvc.yaml:

...
stages:
  version_data:
    cmd: python src/dc/index.py
    outs:
    - data/dataset.parquet

in src/dc/index.py:

from datachain import DataChain, C

(
    DataChain
        .from_storage("s3://dvc-public-versioned/get-started-pools/", type="image", anon=True)
        .filter(C("file.path").glob("*.jpg") | C("file.path").glob("*.png"))
        .to_parquet("data/dataset.parquet")
)

This seems to be a very common operation and it's better to support this out of the box in dvc.yaml file level. It can look like this without any python code:

...
stages:
  version_data:
    - datachain: "s3://dvc-public-versioned/get-started-pools/**/*.{jpg,jpeg,png}"
         outs: "data/dataset.parquet"
         anon: True

PS: it should also be compatible with SaaS version of DC import