Bump version to 0.5.0rc0

[ethanwharris]

What does this PR do?

Fixes # (issue)

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[codecov]

Codecov Report

Merging #717 (10d02b8) into master (21da84d) will decrease coverage by 27.50%.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##           master     #717       +/-   ##
===========================================
- Coverage   89.38%   61.88%   -27.51%     
===========================================
  Files         197      197               
  Lines       10512    10512               
===========================================
- Hits         9396     6505     -2891     
- Misses       1116     4007     +2891     

Flag	Coverage Δ
unittests	61.88% <100.00%> (-27.51%)	⬇️

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

Impacted Files	Coverage Δ
flash/__about__.py	100.00% <100.00%> (ø)
flash/core/utilities/flash_cli.py	22.52% <0.00%> (-77.48%)	⬇️
flash/core/serve/dag/visualize.py	19.04% <0.00%> (-76.20%)	⬇️
flash/core/serve/component.py	21.69% <0.00%> (-72.65%)	⬇️
...ash/pointcloud/segmentation/open3d_ml/backbones.py	20.83% <0.00%> (-70.84%)	⬇️
...ash/core/integrations/vissl/transforms/__init__.py	33.33% <0.00%> (-66.67%)	⬇️
...sh/core/integrations/vissl/transforms/multicrop.py	24.24% <0.00%> (-66.67%)	⬇️
flash/text/question_answering/model.py	25.36% <0.00%> (-65.22%)	⬇️
flash/image/detection/serialization.py	26.92% <0.00%> (-63.47%)	⬇️
...tcloud/segmentation/open3d_ml/sequences_dataset.py	20.18% <0.00%> (-62.39%)	⬇️
... and 111 more

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