Model save in RBM

[pradnyeshjoshi]

Description

1. Added save function to rbm.py: This writes model checkpoints to a specified directory.
2. Added load function to rbm.py: This gives users ability to instantiate a model class, load checkpoints from a pretrained model and resume training.
3. Added code snippet for how to use save and load functions to the RBM quick start notebook.

Related Issues

1. [FEATURE] Model save in RBM #878
2. [FEATURE] Export RBM model #1510

Checklist:

• I have followed the contribution guidelines and code style for this project.
• I have added tests covering my contributions.
• I have updated the documentation accordingly.
• This PR is being made to staging branch and not to main branch.

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Codecov Report

Merging #1618 (6bf139c) into staging (9dec57e) will decrease coverage by 0.01%.
The diff coverage is 73.91%.

❗ Current head 6bf139c differs from pull request most recent head 950172d. Consider uploading reports for the commit 950172d to get more accurate results

@@             Coverage Diff             @@
##           staging    #1618      +/-   ##
===========================================
- Coverage    59.12%   59.10%   -0.02%     
===========================================
  Files           88       88              
  Lines         8942     8953      +11     
===========================================
+ Hits          5287     5292       +5     
- Misses        3655     3661       +6     

Flag	Coverage Δ
pr-gate	59.10% <73.91%> (-0.02%)	⬇️

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Impacted Files	Coverage Δ
recommenders/models/rbm/rbm.py	80.00% <73.91%> (-2.25%)	⬇️

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[miguelgfierro]

this is amazing @pradnyeshjoshi, brutal timing!

Just a minor comment with tests

[miguelgfierro]

Vamos!!!