Allow to change the main model directory name like staging_folder_name

### Describe the feature
I would like to request a feature that allows changing the main `models` directory name in the package, similar to how we can change the `staging_folder_name` using a variable. This would provide greater flexibility for structuring DBT projects, especially for teams that may follow different conventions or naming standards across projects.

### Describe alternatives you've considered
The primary alternative is manually renaming the `models` directory, but this approach is not ideal as it requires adjustments in multiple parts of the project configuration. Additionally, manually changing the folder name may introduce issues with path references and the packages internal workings that expect the default directory name to be `models`.

### Who will this benefit?
This feature will be useful for DBT users who have complex model directory structures or who need to follow specific naming conventions across multiple DBT projects.
For example:

- Teams working across multiple DBT projects may want to standardise or differentiate folder names to improve clarity and maintainability.
- Users following specific naming standards set by their organisation.

### Are you interested in contributing this feature?
I'm interested in contributing this feature and would appreciate guidance on getting started.