Support both yaml and yml file extension for project config files

[morgan-dgk]

Resolves #5002, #8738

Problem

From relevant faq:

At present, dbt will only search for files with a .yml file extension. In a future release of dbt, dbt will also search for files with a .yaml file extension

This behaviour is potentially confusing to new users and runs against the official recommendations in the yaml faq. I was certainly confused by this when I first started working with dbt and ran into errors finding dbt project configuration fils such as profiles.yaml and dbt_project.yaml.

Solution

Failing tests are currently due to hardcoded file names in assertions where tests are expected to fail.

This PR introduces a new helper function get_yaml_path in the yaml_helper module. Given the path to a stem (i.e the path to a yaml file without any extension), this function attempts to finding a matching yaml file ending in either of the accepted extensions, i.e. .yml or .yaml. If no match is found, an empty string is returned.

So as to minimise the changes required to existing code, I also removed the .yml extension from the relevant constants in the dbt/constants module.

I initially considered implementing this somewhere in dbt_common following previous guidance provided on #5002 but the structure of the project appears to have changed since those comments were made. Additionally, there is some variance in how paths to config files are resolved.

For example, some project file paths are defined as constants whereas profiles.yml is passed directly as a string to os.path.join in profiles.yml. In the majority of cases, the path to project files appears to be passed around as a string, but in tasks/base.py.

Using the new helper function as a wrapper to existing calls to resolve the path for relevant config files seemed the least likely to break existing behaviour.

See also comments on #5002.

2e938d7 is an unrelated change, but I could not get pre-commit hooks to work correctly without this change. I believe the underlying issue relates to changes in metadata lib in python 3.12

Checklist

• [ x ] I have read the contributing guide and understand what's expected of me.
• [ x ] I have run this code in development, and it appears to resolve the stated issue.
• [ ] This PR includes tests, or tests are not required or relevant for this PR.
• [ x ] This PR has no interface changes (e.g., macros, CLI, logs, JSON artifacts, config files, adapter interface, etc.) or this PR has already received feedback and approval from Product or DX.
• [ x ] This PR includes type annotations for new and modified functions.

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