For each FRU, vpd-manager launches an extra unnecessary asynchronous task(and potentially nested thread)

[souvik1914581]

Context:

1. vpd-manager calls Worker::collectFrusFromJson() to parse and publish VPD of all FRUs.
2. Worker::collectFrusFromJson() iterates through the list of FRUs in System Config JSON and launches a detached thread for VPD collection of each FRU.
3. Within the body of this detached thread, we are calling std::async with default launch policy, in order to parse and publish the VPD of a FRU in an asynchronous manner. See Worker::collectFrusFromJson()

Issue:

1. Calling std::async inside the detached thread for a FRU and then collecting the result in a std::future is an unnecessary performance overhead.
2. Calling std::async without specifying launch policy may potentially launch another thread. See std::async
3. std::async may throw some exceptions. Worker::collectFrusFromJson() doxygen does not capture this.

As we already have a dedicated detached thread for collecting VPD of a FRU, we should just parse and publish the VPD for this FRU in a synchronous manner from the thread.