Cleanup YAML project code.

[agorajek]

Summary

Few things in this PR:

1. Added update_if_exists flag to namespace and tag creation.
2. Made the above flag default to False everywhere. It used to be True on the node, which I think is not great default. cc @anhqle
3. Added system project namespace cleanup when run inside validation.

Test Plan

Unit tests and my local examples.

• [ ] PR has an associated issue: #
• [ ] make check passes
• [ ] make test shows 100% unit test coverage

Deployment Plan

Asap.

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[agorajek]

Changes largely LGTM!

Only one comment:

Made the above flag default to False everywhere. It used to be True on the node, which I think is not great default.

@agorajek From what I've seen, a lot of people seem to rely on this flag being true... of course we can announce that this is a breaking change, but I'm wondering if that's just the default behavior that people expect or prefer?

@shangyian I am worried that the current setup (created_node --> update_if_exists=True) will lead to silent overrides. I think I could do the following:

• keep this change, create_node( ..., update_if_exists: default False) and
• add a new method to the client create_or_update_node( ..., update_if_exists: default True) This should make it easy for users to pick the expected behavior easily. cc @anhqle

Thoughts?

[agorajek]

I'm good with changing the default of update_if_exists to False.

In that case, it'd be nice to tell user about the update_if_exists functionality when they run into node-already-exists-error.

Yes, we have that already, example:

datajunction.exceptions.DJClientException: Node `default.account_type_table` already exists. Use `update_if_exists=True` to update the node.