🚨🚨🚨 Fix UperNet model and add pretrained checkpoints

[qubvel]

checkpoints: https://huggingface.co/collections/smp-hub/upernet-67fadcdbe08418c6ea94f768

[codecov]

Codecov Report

Attention: Patch coverage is 98.21429% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
segmentation_models_pytorch/base/model.py	0.00%	1 Missing ⚠️

Files with missing lines	Coverage Δ
segmentation_models_pytorch/base/initialization.py	100.00% <100.00%> (ø)
...ntation_models_pytorch/decoders/upernet/decoder.py	98.68% <100.00%> (+0.64%)	⬆️
...mentation_models_pytorch/decoders/upernet/model.py	100.00% <ø> (ø)
...entation_models_pytorch/encoders/timm_universal.py	80.45% <100.00%> (+0.22%)	⬆️
segmentation_models_pytorch/base/model.py	83.56% <0.00%> (ø)

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.