Replaces .project_id with .id to identify the project id value

[Amphagory]

Updating documentation to reflect what project id identifier should be.

An error popped with when I plan the resource dbtcloud_snowflake_credential following its documentation as follows:

│ Error: Unsupported attribute │ │ on credentials.tf line 2, in resource "dbtcloud_snowflake_credential" "test": │ 2: project_id = dbtcloud_project.test.project_id

Looking at the dbtcloud_project documentation, it should be just id

[b-per]

Thanks! I will get it merged shortly!