Adding support for OAuth2 Client Credentials Flow + dependency upgrades

[dervism]

Added support for OAuth2 Client Credentials Flow. See new OpenSkyAuthentication.java. Adds a new constructor to OpenSkyApi:

OpenSkyApi api = new OpenSkyApi(new OpenSkyAuthentication("clientId", "clientSecret"));
    OpenSkyStates os = api.getStates(0, null,
            new OpenSkyApi.BoundingBox(45.8389, 47.8229, 5.9962, 10.5226));

    os.getStates().forEach(System.out::println);

Additional changes:

• Upgraded all build dependencies
• Upgraded tests to JUnit Jupiter
• Updated deprecated method dc.mappingException(...) to JsonMappingExpception
• Bumps the Java release version to 17
• Bumps the library version to 1.4.0