[MPL] Add overloaded operator functions at medium, phase, and component levels

As titled, an overloaded operator[] function is added at medium, phase, and component levels to enhance code readability and ease of implementation. In addition, this pull request also provides a small demo in the ComponentTransportProcess to demonstrate the changes brought by the added operator[] function.

Once this pull request gets consent, the corresponding changes will be extended to all the processes and the original property getter function will be deprecated.

1. Feature description was added to the changelog
2. Tests covering your feature were added?
3. Any new feature or behavior change was documented?