[feat] add support for metadata + resize Semantic Segmentation Image

[tchaton]

What does this PR do?

This PR adds support for metadata and resize the predicted label images.

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[codecov]

Codecov Report

Merging #290 (8349d40) into master (41b9850) will increase coverage by 0.09%.
The diff coverage is 95.12%.

@@            Coverage Diff             @@
##           master     #290      +/-   ##
==========================================
+ Coverage   88.39%   88.49%   +0.09%     
==========================================
  Files          74       74              
  Lines        3612     3642      +30     
==========================================
+ Hits         3193     3223      +30     
  Misses        419      419              

Flag	Coverage Δ
unittests	88.49% <95.12%> (+0.09%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
flash/vision/segmentation/data.py	88.75% <81.81%> (+<0.01%)	⬆️
flash/core/model.py	89.75% <100.00%> (ø)
flash/data/batch.py	82.35% <100.00%> (+1.73%)	⬆️
flash/data/data_source.py	96.87% <100.00%> (+0.02%)	⬆️
flash/vision/segmentation/model.py	92.72% <100.00%> (+2.02%)	⬆️
flash/vision/segmentation/serialization.py	82.60% <100.00%> (+0.38%)	⬆️

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[ethanwharris]

LGTM 😃 small typo