Improve LightningDataModule hook test and fix dataloader_idx argument

[carmocca]

What does this PR do?

• Create HookedDataModule to append the called hooks dynamically. Any new hook will make the test fail. We want this so there's no forgetting to update the test.
• The hook arguments are now tested
• A small fix is included to only include the dataloader_idx argument during predict if there is more than one dataloader. This is consistent with the rest of the loops.

Related to the Lightning hooks review: #7740

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[codecov]

Codecov Report

Merging #7941 (09c83eb) into master (20a5e09) will decrease coverage by 0%.
The diff coverage is 100%.

@@          Coverage Diff           @@
##           master   #7941   +/-   ##
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- Coverage      92%     91%   -0%     
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  Files         203     203           
  Lines       13129   13125    -4     
======================================
- Hits        12017   11974   -43     
- Misses       1112    1151   +39     

[tchaton]

LGMT !