Alpha Release 0.0.4

What's Changed

• Reduce restrictions on pipeline model structure by @rhazn in #70
• Clear existing data in SQL sinks by @felix-oq in #72
• Add CLA workflow by @georg-schwarz in #74
• Fixed a bug with empty column names in postgres by @rhazn in #75

Full Changelog: v0.0.3-alpha...v0.0.4-alpha