Add bus-env REST controller for multiple properties

[yashdotdev13]

Summary

This PR adds a REST controller for the /actuator/bus-env endpoint that supports updating multiple environment properties in a single request.

Changes

• Add EnvironmentBusController using @RestControllerEndpoint.
• Accept multiple properties through @RequestParam Map<String, String>.
• Replace the existing EnvironmentBusEndpoint registration with the new REST controller.
• Add unit coverage for publishing multiple properties.
• Add integration coverage for the /actuator/bus-env HTTP endpoint.

Testing

• EnvironmentBusControllerTests
• EnvironmentBusControllerIntegrationTests

Both tests pass successfully.

Fixes #122

[ryanjbaxter]

Why not add this to the existing endpoint? We should not remove the existing one at all.