Add slack analytics project

[MajaCernja]

Description

WIP PR adding a slack_analytics dbt project containing a few models and macros for processing message and reactions data accessible via the public Slack API.

TO-DO

• Generate dummy raw data and create a .duckdb file
• Set up a few tasks! Some ideas: remove fct model and ask to generate it from scratch, break / omit a macro and request fix, introduce inaccuracies in _models.yml (schema.yml)

[bstancil]

hey @MajaCernja , welcome! This would be great to include, if you're got ideas for generating data or for tasks. (I'm also working on generated data for a larger dbt project, so if I end up creating a programmatic way to do that, I can share it with you)