(fix) Add support for attaching a MotherDuck database with token in settings or config

[guenp]

Add support for attaching a MotherDuck database and pass an arbitrary token via config, settings or path.

Example profiles.yml:

test:
  outputs:
    user:
      threads: 1
      type: duckdb
      path: /tmp/data.duckdb
      attach:
       - path: md:my_db
         type: motherduck
      settings:
        motherduck_token: "{{ env_var('motherduck_token_1') }}"

Right now, this fails with an error:

Runtime Error
  setting 'motherduck_token' can only be set during initialization

This is because the SET command happens after the ATTACH. Similarly, when passing the token via config, this also fails, because the motherduck extension is not yet loaded when running duckdb.connect. Lastly, passing the token via the path also fails because it's passed to the ATTACH command directly and this also does not let you set the token.

Therefore, currently the only way to attach a MotherDuck database is to have the motherduck_token env var set.

After some discussion with Josh we decided:

• re-order the attach block and the plugin initialization block inside of initialize_db (so that plugins were initialized before attaches)
• SET the MotherDuck token before the md: attach happens. Similar to how the config is updated when connecting to a MD path.

[jwills]

looks good to me @guenp!