Added Azure Cognitive Search vector store (#7469)

.vscode/settings.json

CHANGELOG.md

docs/community/integrations/vector_stores.md

docs/core_modules/data_modules/storage/customization.md

docs/core_modules/data_modules/storage/vector_stores.md

docs/examples/vector_stores/CognitiveSearchIndexDemo.ipynb

llama_index/vector_stores/__init__.py

llama_index/vector_stores/cogsearch.py

tests/vector_stores/test_cogsearch.py