miscellaneous changes

As part of this PR,

1. using the BlobStore class from azure-core-lib. Removing the local implementation/ updated UTs
2. Using createItem method instead of upsertItem from cosmosStore class wherever applicable. Updated UTs
3. Updated README to add instructions to run Integration tests.
4. Added script to generate JWT in azure. To be consumed by deployment scripts

FYI @polavishnu , @kibattul