Adds support for COPY TO/FROM Azure Blob Storage

[aykut-bozkurt]

Supports following Azure Blob uri forms:

• az://{container}/key
• azure://{container}/key
• https://{account}.blob.core.windows.net/{container}/key

Configuration

The simplest way to configure object storage is by creating the standard ~/.azure/config file:

$ cat ~/.azure/config
[storage]
account = devstoreaccount1
key = Eby8vdM02xNOcqFlqUwJPLlmEtlCDXJ1OUzFT50uSRZ6IFsuFq2UVErCz4I6tq/K1SZFPTOtr/KBHBeksoGMGw==

Alternatively, you can use the following environment variables when starting postgres to configure the Azure Blob Storage client:

• AZURE_STORAGE_ACCOUNT: the storage account name of the Azure Blob
• AZURE_STORAGE_KEY: the storage key of the Azure Blob
• AZURE_STORAGE_SAS_TOKEN: the storage SAS token for the Azure Blob
• AZURE_CONFIG_FILE: an alternative location for the config file

Bonus Additionally, PR supports following S3 uri forms:

• s3://{bucket}/key
• s3a://{bucket}/key
• https://s3.amazonaws.com/{bucket}/key
• https://{bucket}.s3.amazonaws.com/key

Closes https://github.com/CrunchyData/pg_parquet/issues/50