chore: add unit tests for MediaType class

[Mohammad-Dwairi]

Situation

With the introduction of the new SDK core, we need to raise the tests coverage before attempting to migrate the core module to the original repository. We will be testing the new core with this LC SDK during this temporary phase.

Task

1. Cover MediaType HTTP model class with unit tests

Action

1. Refactored the original MediaType class for better clarity.
2. Added CommonMediaTypes utility class that holds common media types used usually as Content-Type header value.
3. Updated LoggableMediaTypes to use the refactored MediaType instances.
4. Added MediaTypeTest with Kotlin tests.
5. Added MediaTypeJavaTest with Java tests, mainly to ensure Java accessibility and usability.
6. Added CommonMediaTypesTest Kotlin tests.

Testing

All tests are passing

Results

MediaType & CommonMediaTypes are 100% covered