fw_update: Introduce AggregateUpdateManager

Description:
This commit introduces the `AggregateUpdateManager` class for handling
multiple firmware update sessions simultaneously. The
`AggregateUpdateManager` acts as a reverse proxy for PLDM messages,
routing them to the appropriate `UpdateManager` instance based on the
`instanceId`. This allows for concurrent firmware updates, improving
the efficiency and flexibility of the firmware update process.

Motivation:
We have introduced the `FirmwareInventory`/`FirmwareInventoryManager`
classes to manage D-Bus interfaces for firmware update, After that, we
would like to implement the `StartUpdate` method for `FirmwareInventory`
properly for the update process implementation[1], which
`AggregateUpdateManager` will help route the command to the specific
update sessions.

Details of the PLDM message reverse proxy:
By the implementation, different update session would be handled with
different `instanceId`s, which can help `UpdateManager`s to identify
whether the message is for them or not.
Whenever a PLDM response message is received, the flow that
the `AggregateUpdateManager` do:
 1. Handle the message for existing update flow if the instance_id
    (the pldm instance numbers) matches the update task which using the
    existing update flow.
 2. Traverse forward the message to each `ItemUpdateManager`
    (implementation in the next patch) instances if there's no match in
    step 1.
 3. Return error message PLDM_FWUP_COMMAND_NOT_EXPECTED if no matches in
    step 2.

[1]: https://gerrit.openbmc.org/c/openbmc/pldm/+/74774

Change-Id: Icfdb8d238121f9f44a624396e00b378e491ce652
Signed-off-by: Unive Tien <unive.tien.wiwynn@gmail.com>
diff --git a/fw-update/update_manager.hpp b/fw-update/update_manager.hpp
index 5aa80ec..4320de1 100644
--- a/fw-update/update_manager.hpp
+++ b/fw-update/update_manager.hpp
@@ -47,7 +47,7 @@
     UpdateManager(UpdateManager&&) = delete;
     UpdateManager& operator=(const UpdateManager&) = delete;
     UpdateManager& operator=(UpdateManager&&) = delete;
-    ~UpdateManager() = default;
+    virtual ~UpdateManager() = default;
 
     explicit UpdateManager(
         Event& event,
@@ -80,8 +80,8 @@
      *
      *  @return PLDM response message
      */
-    Response handleRequest(mctp_eid_t eid, uint8_t command,
-                           const pldm_msg* request, size_t reqMsgLen);
+    virtual Response handleRequest(mctp_eid_t eid, uint8_t command,
+                                   const pldm_msg* request, size_t reqMsgLen);
 
     int processPackage(const std::filesystem::path& packageFilePath);