Create schema for external tables when it is not there.

[guillesd]

Description & motivation

Addresses https://github.com/dbt-labs/dbt-external-tables/issues/100 for the following adapters:

• SQL Server
• Spark
• BigQuery
• Snowflake It was mentioned in the issue by @jtcohen6 that external schemas in Redshift are quite a complicated thing, so the macro is not supported for their adapter and it is not included in the build plan.

Checklist

• [x] I have verified that these changes work locally (only for Spark)
• [x] I have updated the README.md (if applicable)
• [x] I have added an integration test for my fix/feature (if applicable)

Details

The create_external_schema macro is created, which takes in a source_node and creates the schema. The macro is added to the build_plan so that the process is more explicit (and logged). This macro is common for Snowflake, Spark and BigQuery and is overwritten in the SQL Server adapter. I did not use the create_schema default macro of dbt since it takes in a different argument than a source_node and I did not want to overwrite such a core macro for this.

Hope you liked my approach!

[guillesd]

@jeremyyeo tagging you for visibility! @pgoslatara

[guillesd]

@jeremyyeo does this need something to be merged?

[guillesd]

@jeremyyeo Fixed the wrong reference to the docs. Anything else?

[taskooh]

Hello, I am waiting for this PR to be merged, but is there any problem?

[taskooh]

@jeremyyeo @jtcohen6 Hello, when will this PR Merged? I'm waiting for this feature

[jeremyyeo]

Thanks @guillesd - appreciate the contribution and apologies for taking forever to merge this :P