Add CI for Siamese Network Example

[DeepC004]

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Fixes #2878

Description: Adds unit test for Siamese Network example, updated README and minor changes

Check list:

• [x] New tests are added (if a new feature is added)
• [ ] New doc strings: description and/or example code are in RST format
• [x] Documentation is updated (if required)

[vfdev-5]

@DeepC004 sorry for delay and I just checked the runtime and this example adds +10 minutes of CI runtime. Let's try to reduce that

[DeepC004]

Hi, one way to reduce the training time can be increasing the batch size. I am unaware of the memory limits of the remote host used for CI, hence one way to try is to keep increasing the train and test batch size in powers of 2. Also, training time is the bottleneck hence increasing the num_workers while dataloading will not make difference, nevertheless I will play around to see if there are any improvements in runtime.