Add dedicated patch and delete item functions

[mdwRepository]

The DSpaceClient class lacks a full patch_item method to facilitate partial updates for Item objects via the REST API. To address this, we propose implementing a patch_item function that supports add, remove, and replace operations, excluding move.

Supported operations:

• add: Adds new metadata or fields to the object.
• remove: Removes specified metadata or fields.
• replace: Replaces the value of existing metadata or fields.

Validation:

• Ensures the provided object is a valid Item.
• Verifies that the operation is one of the supported types.
• Requires a value for add and replace operations.

The DSpaceClient class also lacks a delete_item method for deleting Item objects via the REST API. To address this, we propose implementing a delete_item function that uses the existing api_delete functionality to perform deletions efficiently and reliably.

Validation:

• Ensures the provided object is a valid Item.
• Confirms the existence of a valid self link in the Item object.