Add fixture for Cal-ITP Staff account

[thekaveman]

This would be similar to the task from: #2370 (review)

I.e. running the site locally, we should seed the database with a calitp-user or similar, to make testing and QA a little simpler without having to manually set up user accounts.

Acceptance Criteria

• The local_fixtures.json include a definition for a sample user that is a member of the Cal-ITP staff group
• The sample user details are stored in the same shared LastPass area as e.g. the sample cst-user

Additional context

Would be helpful in reviewing e.g. #2671