📝 Update schema graphic & clarify metadata schema vs. datasets schema

[falexwolf]

Before	After

Slack thread.

% lamin save schema-lamindb-v0.76.6.png --key exemplary-schema.png --description schema-lamindb-v0.76.6
→ connected lamindb: laminlabs/lamin-site-assets
→ creating new artifact version for key='exemplary-schema.png' (storage: 's3://lamin-site-assets')
... uploading schema-lamindb-v0.76.6.png: 100.0%
→ saved: Artifact(uid='XoTQFCmmj2uU4d2xyj9u', is_latest=True, description='schema-lamindb-v0.76.6', key='exemplary-schema.png', suffix='.png', size=600326, hash='pAW2zmGIh2SoAIJbxVvcIQ', _hash_type='md5', visibility=1, _key_is_virtual=True, storage_id=1, created_by_id=1, updated_at='2024-09-17 21:38:26 UTC')
→ storage path: s3://lamin-site-assets/.lamindb/XoTQFCmmj2uU4d2xyj9u.png
→ go to: https://lamin.ai/laminlabs/lamin-site-assets/artifact/XoTQFCmmj2uU4d2xyj9u
→ storage url: https://lamin-site-assets.s3.amazonaws.com/.lamindb/XoTQFCmmj2uU4d2xyj9u.png