Use elegant way to get all features for a project and fix potential concurrency issues

[xiaoyongzhu]

This PR addresses a few comments/issues:

1. Previously, when getting all the features for a certain project, we use search_entities method, which might not be scalable when there are tons of entities (or might take some time)
2. We use the attribute field to get the relations between different entities (between project and anchor, or between derived features, etc.), which might be hard to merge two projects.

This PR solves those two issues, by doing the following:

1. Using lineage API to get all the entities belonging to a certain project at once, so that we don't have to do search, rather we rely on the pre-computed purview lineage to get all the entities
2. when calling get_features_from_registry(), we don't use the attributes since there might be concurrency issues; Instead, we use AtlasProcess to avoid potential concurrency issues.

Also fixed an issue brought by #380 where additional schema is added.

[xiaoyongzhu]

#466 the issues should already be fixed by this PR hence closing.