Update the download_demo and get_available_demos functions

[fealho]

CU-86b6fugf3, Resolve #2661.

[sdv-team]

Task linked: CU-86b6fugf3 SDV - Add get_source and get_readme functions for demo datasets #2663

[codecov]

Codecov Report

❌ Patch coverage is 93.57798% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 98.06%. Comparing base (1705ced) to head (7706a5a).
⚠️ Report is 1 commits behind head on feature-branch-download-demo.

Files with missing lines	Patch %	Lines
sdv/datasets/demo.py	93.51%	7 Missing ⚠️

Additional details and impacted files

@@                       Coverage Diff                        @@
##           feature-branch-download-demo    #2669      +/-   ##
================================================================
- Coverage                         98.13%   98.06%   -0.07%     
================================================================
  Files                                70       70              
  Lines                              7493     7556      +63     
================================================================
+ Hits                               7353     7410      +57     
- Misses                              140      146       +6     

Flag	Coverage Δ
integration	75.95% <78.89%> (-0.38%)	⬇️
unit	96.75% <86.23%> (-0.15%)	⬇️

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