resolves
#341
dbt-labs/dbt-core#11334

Description

If I've configured my seed's column names in a yml file, I don't want to also keep a header row up-to-date in my csv seed file.

seeds:
  - name: my_seed
    columns:
      - name: country_code
        data_type: varchar(2)
      - name: country_name
        data_type: varchar(32)

country_code,country_name
US,United States
CA,Canada
GB,United Kingdom

Instead, I should be able to configure my seed to not need a header row if I've configured my column names in yml already.

seeds:
  - name: my_seed
    config:
      header: false
    columns:
      - name: country_code
        data_type: varchar(2)
      - name: country_name
        data_type: varchar(32)

US,United States
CA,Canada
GB,United Kingdom

Checklist

• I have read the contributing guide and understand what's expected of me
• I have signed the CLA
• I have run this code in development and it appears to resolve the stated issue
• I have opened an issue to add/update docs, or docs changes are not required/relevant for this PR
• I have run changie new to create a changelog entry