[Cosmos] Item Create/Update/Delete

[analogrelay]

#1809 will add querying for Cosmos Items. We need to add the ability to create/update/delete items. The API would be something like this, based on the Go SDK:

pub trait ContainerClientMethods {
    // ... other methods ...
    // Will fail if an item with the same ID already exists (POST with Upsert header false)
    fn create_item(&self, partition_key: impl Into<PartitionKey>, item: impl Serialize, options: Option<CreateItemOptions>);
    // Will replace an item with the same ID if one exists (POST with Upsert header true)
    fn upsert_item(&self, partition_key: impl Into<PartitionKey>, item: impl Serialize, options: Option<UpsertItemOptions>);
    // Will fail if an item with the same ID does NOT exist (PUT)
    fn replace_item(&self, partition_key: impl Into<PartitionKey>, item: impl Serialize, options: Option<ReplaceItemOptions>);
    // Will fail if an item with the specified ID does not exist (DELETE)
    fn delete_item(&self, partition_key: impl Into<PartitionKey>, item_id: impl Into<String>, options: Option<DeleteItemOptions>);
}

Notable exclusions: PATCHing documents (requires modelling the patch operations and will be handled separately)

Open Questions:

• Does each operation need it's own options? The Go SDK uses a single shared ItemOptions. We can do the same, but if we ever need operation-specific options, it's a breaking change. I'll check if the other SDKs generally accept that risk and use a shared options type. If they do, I think we can here as well.