Gracefully handle invalid states when filtering environments

What does this MR do and why?

This merge request handles Environments::EnvironmentsFinder::InvalidStatesError exception gracefully to return a bad request (400) response instead of an internal server error (500) when trying to filter environments with an invalid states value (allowed values are: available and stopped).

Fixes (#360138 (closed)).

How to set up and validate locally

1. Start GDK locally, if it isn't up already: gdk start.
2. Make sure one of the projects on your local installation has an environment configured.
3. In your terminal, send a request to the /environments endpoint (using your preferred method of API authentication) as follows:

echo -e | curl -v -X GET  -H "Content-Type: application/json" -H "Authorization: Bearer YOUR_TOKEN" localhost:3000/api/v4/projects/:project_id/environments?states=a

4. Validate that the response has status 400 with the following error message: Requested states are invalid.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.