Rename datasette_metadata_column_entries internal tables to e.g. metadata_columns

[simonw]

Currently the internal metadata tables are called:

• datasette_metadata_column_entries
• datasette_metadata_instance_entries
• datasette_metadata_resource_entries
• datasette_metadata_database_entries

But the catalog tables are:

• catalog_columns
• catalog_databases
• catalog_foreign_keys
• catalog_indexes
• catalog_tables

Renaming the metadata columns like so would be more consistent:

• metadata_instance - singular because there is only one instance
• metadata_databases
• metadata_resources
• metadata_columns

[simonw]

I'm going to add the schema to the documentation too, using Cog - it will go here: https://docs.datasette.io/en/latest/internals.html#datasette-s-internal-database

[simonw]

I shipped this to a Datasette Cloud test instance running datasette-visible-internal-db and it worked: