Add Padding image preprocessor

[zaleslaw]

The Padding image preprocessor is missed in KotlinDL.
Pad the given image on all sides with the given “pad” value.

The desired PR addressing this issue should include:

• Implementation (you can take inspiration from the implementation of Cropping as reference)
• Documentation
• JUnit tests in dataset module
• An example with usage of this image preprocessor

P.S. If you want to take this ticket, please leave the comment below
P.P.S Read the Contributing Guidelines.

The reference implementation could be taken from torchvision.transforms

[zaleslaw]

@juliabeliaeva could you have a look at this issue?

[juliabeliaeva]

@zaleslaw yes, assign this issue to me, please.