Adds environment type indicator to admin bar

[psorensen]

Description of the Change

This adds a display to the admin bar to indicate the current environment type based on the WP_ENVIRONMENT_TYPE config variable. Most useful for increasing awareness and preventing inadvertent changes to production environment. Inspired by Display Environment Type plugin.

Closes #147

How to test the Change

Configure different environment types and observe that changes to indicator match.

Changelog Entry

Added - New feature Changed - Existing functionality Deprecated - Soon-to-be removed feature Removed - Feature Fixed - Bug fix Security - Vulnerability Added indicator to admin bar to denote current environment type.

Credits

Props @username, @username2, ... @psorensen @rickalee

Checklist:

• [x] I agree to follow this project's Code of Conduct.
• [x] I have updated the documentation accordingly.
• [ ] I have added tests to cover my change.
• [x] All new and existing tests pass.