Support global distribution configuration with Cosmos KV SDK

[kate-goldenring]

Cosmos DB supports configuring global replication of data; however, it is up to the client to specify which region to query data from by specifying preferredRegion in requests. When many language SDKs support this (Go, Java, Python, C#), the Rust SDK does not appear to support it. We will potentially need to add support there first in order to pull it into Spin

[kate-goldenring]

Breaking this down, we essentially want to determine or enable configuring the region specific URL. For example, if your database is named foo and exists in westus and eastus, the URLs are as follows:

• westus: https://foo-westus.documents.azure.com:443/
• eastus: https://foo-eastus.documents.azure.com:443/
• base/default: https://foo.documents.azure.com:443/

We should at least enable configuring the region in the runtime config and then suffix that on the URL. A more comprehensive API would query the base URL in order to get the account properties. The following is an example response from the Azure docs:

{
    "_dbs": "//dbs/",
    "media": "//media/",
    "writableLocations": [
        {
            "Name": "West US",
            "DatabaseAccountEndpoint": "https://globaldbexample-westus.documents.azure.com:443/"
        }
    ],
    "readableLocations": [
        {
            "Name": "East US",
            "DatabaseAccountEndpoint": "https://globaldbexample-eastus.documents.azure.com:443/"
        }
    ],
    "MaxMediaStorageUsageInMB": 2048,
    "MediaStorageUsageInMB": 0,
    "ConsistencyPolicy": {
        "defaultConsistencyLevel": "Session",
        "maxStalenessPrefix": 100,
        "maxIntervalInSeconds": 5
    },
    "addresses": "//addresses/",
    "id": "globaldbexample",
    "_rid": "globaldbexample.documents.azure.com",
    "_self": "",
    "_ts": 0,
    "_etag": null
}

This could be used to confirm that the region is in fact available