Update TensorboardGenerativeModelImageSampler args

[chris-clem]

What does this PR do?

Updates TensorboardGenerativeModelImageSampler args as discussed in #489.

Fixes #489

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[codecov]

Codecov Report

Merging #494 (1bf5420) into master (42cfa8f) will decrease coverage by 0.17%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #494      +/-   ##
==========================================
- Coverage   79.24%   79.06%   -0.18%     
==========================================
  Files         107      102       -5     
  Lines        6201     5919     -282     
==========================================
- Hits         4914     4680     -234     
+ Misses       1287     1239      -48     

Flag	Coverage Δ
cpu	25.76% <18.18%> (-0.35%)	⬇️
pytest	25.76% <18.18%> (-0.35%)	⬇️
unittests	78.57% <100.00%> (-0.21%)	⬇️

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

Impacted Files	Coverage Δ
pl_bolts/callbacks/vision/image_generation.py	93.33% <100.00%> (+2.02%)	⬆️
pl_bolts/utils/__init__.py	100.00% <0.00%> (ø)
pl_bolts/callbacks/__init__.py	100.00% <0.00%> (ø)
pl_bolts/models/rl/dqn_model.py	78.98% <0.00%> (ø)
pl_bolts/models/self_supervised/__init__.py	100.00% <0.00%> (ø)
...l_bolts/models/self_supervised/swav/swav_resnet.py	70.20% <0.00%> (ø)
...bolts/models/self_supervised/amdim/amdim_module.py	96.73% <0.00%> (ø)
pl_bolts/callbacks/verification/batch_gradient.py
pl_bolts/callbacks/verification/base.py
...s/models/self_supervised/simsiam/simsiam_module.py
... and 12 more

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[akihironitta]

@chris-clem Thank you for your swift action! Would you mind having a look at the below suggestions?

[akihironitta]

@chris-clem LGTM. Thank you!

[akihironitta]

@Borda @ananyahjha93 Should we include the tests for this class in this PR? or later in another PR?