fully remove support - we should not support spaces in model names

[graciegoheen]

Created as a follow up to #9397

Housekeeping

• I am a maintainer of dbt-core

Short description

In 1.8 we began emitting warnings about spaces in model names. In 1.9 we should instead be raising an error. The work done for this for 1.8 (#9886) included a project flag allow_spaces_in_model_names which was defaulted to True. To begin raising errors, this needs to be defaulted to False instead.

Acceptance criteria

• spaces in model names raise errors
  • this is disable-able

Suggested Tests

• default behavior is to raise errors

Impact to Other Teams

N/A

Will backports be required?

N/A

Context

No response

[graciegoheen]

Dupe of #9633