Make eng folder optional in sparse-checkout.yml

[scbedd]

Comment here has context as to why I'm submitting this PR.

[azure-sdk]

The following pipelines have been queued for testing:
java - template
java - template - tests
js - template
net - template
net - template - tests
python - template
python - template - tests
You can sign off on the approval gate to test the release stage of each pipeline.
See eng/common workflow

[azure-sdk]

The following pipelines have been queued for testing:
java - template
java - template - tests
js - template
net - template
net - template - tests
python - template
python - template - tests
You can sign off on the approval gate to test the release stage of each pipeline.
See eng/common workflow

[benbp]

See Azure/azure-sdk-for-python#16667 (comment). I think preferring to use /* which seems to be the "all" glob convention for sparse-checkout is a better approach here, rather than adding another conditional.

Default sparse-checkout file on init, which includes all top level files and excludes sub-directories (so we'll just take the first line):

⇉ ⇉ ⇉ cat .git/info/sparse-checkout
/*
!/*/

[scbedd]

@benbp agree. I tried it with the pattern and it def works.