Improve Airtable import

[simonhammes]

Improvements

• Improved log messages
• Airtable schema is retrieved using Airtable's meta API instead of trying to decude field types from row values
  • Note: This needs the schema.bases:read scope
• Allows excluding specific column types (e.g. files) from data sync
• Allows excluding specific columns from data sync using a list of tuples (table_name, column_name)
• Creates a separate table in the SeaTable base to track columns that need to be manually migrated (e.g. link-formula)

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I also commented out two sleep() statements since Airtable's API seems to be quite slow and I never hit a rate limit. Using a library like requests-ratelimiter might be a more robust option to a) prevent rate limits and b) prevent the migration process from being unnecessarily slow.