Improve LightningCLI documentation and tests

[mauvilsa]

What does this PR do?

• Added cli unit tests for help, print_config and submodules.
• Added to cli documentation use of subclass help and print_config, submodules and other minor improvements.
• Increased minimum jsonargparse version required for new documented features.

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[codecov]

Codecov Report

Merging #7156 (4daf5d4) into master (8439aea) will decrease coverage by 8%.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           master   #7156     +/-   ##
========================================
- Coverage      92%     83%     -8%     
========================================
  Files         197     198      +1     
  Lines       12629   13376    +747     
========================================
- Hits        11611   11161    -450     
- Misses       1018    2215   +1197     

[awaelchli]

lgtm :)

[tchaton]

LGTM !

[tchaton]

Hey @mauvilsa,

Do we think we should consider create a LightningCLIStore.

This would be used to register LightningCLI LightningModule / DataModule.

Example:

# register pair of LightningModule / DataModule
LightningCLIStore.register(VisionModel, MnistDataModule)
LightningCLIStore.register(VisionModel, CIFAR10DataModule)
LightningCLIStore.register(VisionModel, ImagenetteDataModule)
LightningCLIStore.register(VisionModel2, ImagenetteDataModule)


# in train.py
client = LightningCLIStore()

From the command line:

1 / Get the store pairs

python train.py -h 

available:
VisionModel, MnistDataModule
VisionModel, CIFAR10DataModule
VisionModel, ImagenetteDataModule
VisionModel2, ImagenetteDataModule

2 / Filter on the class name

python train.py -h model=visionModel

available:
VisionModel, MnistDataModule
VisionModel, CIFAR10DataModule
VisionModel, ImagenetteDataModule

python train.py -h data= CIFAR10DataModule

available:
VisionModel, CIFAR10DataModule

3 / Normal LightningCLI

python train.py model=VisionModel2 data= ImagenetteDataModule  -h

....

[tchaton]

@mauvilsa Opened a feature request there: #7250.
Happy to get your thoughts.