feat: support azure blob sync

[wilson-matthew]

This PR

• adds support for Azure Blob Storage sync

How to test

• create an Azure Storage Account and a container with a flags definition file inside
• set AZURE_STORAGE_ACCOUNT env var to the name of the storage account
• set AZURE_STORAGE_KEY env var to the access key of the storage account, or use another authentication method: https://pkg.go.dev/gocloud.dev/blob/azureblob#hdr-URLs
• start flagd with the --uri flag set to azblob://my-container/my-flags.json

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[beeme1mr]

Thanks! I'd like to test it out manually before giving a final approval, but it looks good so far. Also, nice job catching all those doc inconsistencies.

[beeme1mr]

Hey @wilson-matthew, I'm new to Azure, so please bear with me. I tried to test using a SAS token but ran into a 403. The environment variable I set was AZURE_STORAGE_SAS_TOKEN, which appears to be supported by the blob library. Do you have any idea what's happening, or should I try a different auth mechanism?

[wilson-matthew]

Hey @beeme1mr, I just tested using a SAS token with the AZURE_STORAGE_SAS_TOKEN environment variable and it worked okay for me. What settings did you use when generating the SAS token - I wonder if it didn’t have the correct permissions? You could try the AZURE_STORAGE_KEY auth mechanism as that is unlikely to have a permissions issue.

[beeme1mr]

I got it working, thanks!