Add load_benchmark_data management command for performance testing

[awais786]

This pull request introduces support for generating and loading benchmark data into the Bakerydemo project by implements GitHub issue #570 . Adds load_benchmark_data management command for performance testing.

# Run with defaults
python manage.py load_benchmark_data

# Create 100K pages for scale testing
python manage.py load_benchmark_data --blog-pages-count=100000

# Full benchmark configuration
python manage.py load_benchmark_data \
  --blog-pages-count=100000 \
  --streamfield-blocks-count=100 \
  --streamfield-depth=10 \
  --inline-panel-items-count=100 \
  --paragraphs-count=100 \
  --revisions-per-page-count=100 \
  --page-tree-depth=10 \
  --images-count=1000 \
  --snippets-count=1000000 \
  --translations-count=100

[awais786]

@thibaudcolas This is basic draft PR. I am planning to add small prs in incremental way. Just want to confirm I am on right track ?

[awais786]

@thibaudcolas Kindly review.