Support loading a 3D model's textures from memory

[johannesugb]

Some 3D models include the texture data directly in the 3D model file. Currently, Gears-Vk only supports loading textures from file during model loading, but the functionality should be extended s.t. they can also be loaded from memory.

These two 3D model files can serve as test subjects (TODO: To be verified):

• https://sketchfab.com/3d-models/tyrannosaurus-rex-9d3a3e42c0054c35aa39c3ee07388d16
• https://sketchfab.com/3d-models/model-56a-southern-white-rhino-8e97b62a90f44ce19ea9e3fd421f55b4

And there's already someone who implemented this, so the following post by alexforever82 is probably helpful: assimp/assimp#408 (comment)

Definition of done:

• 3D model files with integrated textures can be loaded gvk::model_t::load_from_file
• The serializer functionality is supported, i.e. by the means of gvk::create_image_from_file_cached or a similar *_cached function
• The code is well documented and the Contribution Guidelines have been followed.