PartitionKeyDelete: Adds API to delete all items in a partition key

[Shaleen-Kalsi]

PartitionKeyDelete: Add API to delete all items in a partition key

Description

1. Added DeleteItemsInPartitionKeyAsync API
2. Changes in GetStoreProxy in DocumentClient.cs, GetHttpMethod in RequestInvokerHandler.cs, PrepareRequestMessageAsync in GatewayStoreClient.cs for GatewayMode of PkDeletePurger to work.

class Container
{
        /// <summary>
        /// Deletes all items in the Container with the specified <see cref="PartitionKey"/> value.
        /// </summary>
        /// <param name="partitionKey">The <see cref="PartitionKey"/> of the items to be deleted.</param>
        /// <param name="requestOptions">(Optional) The options for the Partition Key Delete request.</param>
        /// <param name="cancellationToken">(Optional) <see cref="CancellationToken"/> representing request cancellation.</param>
        /// <returns>
        /// A <see cref="Task"/> containing a <see cref="ResponseMessage"/>.
        /// </returns>
        public abstract Task<ResponseMessage> DeleteAllItemsByPartitionKeyAsync(
               Cosmos.PartitionKey partitionKey,
               ItemRequestOptions requestOptions = null,
               CancellationToken cancellationToken = default(CancellationToken));
}

[github-actions]

Please follow the required format: "[Internal] Category: (Add|Fix|Refactor) Description"

Examples:
Diagnostics: Add GetElapsedClientLatency to CosmosDiagnostics
PartitionKey: Fix null reference when using default(PartitionKey)
[v4] Client Encryption: Refactor code to external project
[Internal] Query: Add code generator for CosmosNumbers for easy additions in the future.

[github-actions]

Please follow the required format: "[Internal] Category: (Add|Fix|Refactor) Description"

Examples:
Diagnostics: Add GetElapsedClientLatency to CosmosDiagnostics
PartitionKey: Fix null reference when using default(PartitionKey)
[v4] Client Encryption: Refactor code to external project
[Internal] Query: Add code generator for CosmosNumbers for easy additions in the future.

[github-actions]

Please follow the required format: "[Internal] Category: (Add|Fix|Refactor) Description"

Examples:
Diagnostics: Add GetElapsedClientLatency to CosmosDiagnostics
PartitionKey: Fix null reference when using default(PartitionKey)
[v4] Client Encryption: Refactor code to external project
[Internal] Query: Add code generator for CosmosNumbers for easy additions in the future.

All good!

[github-actions]

Please follow the required format: "[Internal] Category: (Adds|Fixes|Refactors) Description"

Examples:
Diagnostics: Adds GetElapsedClientLatency to CosmosDiagnostics
PartitionKey: Fixes null reference when using default(PartitionKey)
[v4] Client Encryption: Refactors code to external project
[Internal] Query: Adds code generator for CosmosNumbers for easy additions in the future.

[github-actions]

Please follow the required format: "[Internal] Category: (Adds|Fixes|Refactors) Description"

Examples:
Diagnostics: Adds GetElapsedClientLatency to CosmosDiagnostics
PartitionKey: Fixes null reference when using default(PartitionKey)
[v4] Client Encryption: Refactors code to external project
[Internal] Query: Adds code generator for CosmosNumbers for easy additions in the future.

[github-actions]

Please follow the required format: "[Internal] Category: (Adds|Fixes|Refactors) Description"

Examples:
Diagnostics: Adds GetElapsedClientLatency to CosmosDiagnostics
PartitionKey: Fixes null reference when using default(PartitionKey)
[v4] Client Encryption: Refactors code to external project
[Internal] Query: Adds code generator for CosmosNumbers for easy additions in the future.

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