Move profiles config to project flags

[dbeatty10]

resolves #925

Problem

The migration guide for v1.8 includes:

• Custom defaults of global config flags should be set in the flags dictionary in dbt_project.yml, instead of in profiles.yml. Support for profiles.yml has been deprecated.

Solution

Move from config: from profiles.yml to flags: in dbt_project.yml.

Checklist

• This code is associated with an issue which has been triaged and accepted for development.
• I have read the contributing guide and understand what's expected of me
• I have run this code in development and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• I have updated the README.md (if applicable)