Share Cosmos connection between Function instances

[ReaNAiveD]

Description

• Use global variables to maintain the Cosmos connections, so that we could reuse the connections and improve performance.
• https://learn.microsoft.com/en-us/azure/azure-functions/manage-connections?tabs=csharp#static-clients

  To avoid holding more connections than necessary, reuse client instances rather than creating new ones with each function invocation. We recommend reusing client connections for any language that you might write your function in. For example, .NET clients like the HttpClient, DocumentClient, and Azure Storage clients can manage connections if you use a single, static client.