Remove Confusion around source packages by introducing a new task

[azlam-abdulsalam]

Source Packages is an idea to bring artifact based deployment (similar to unlocked packaging) but done off the platform and basically to carry over metadata that is not covered by unlocked packages. It is as simple as having a Json metadata with commit id and a version number, which can then be deployed by metadata api.
However the use of this tasks are not straight forward, one have to remember, to checkout the artifact and then deploy the directory.

It is better to have a single task that handles installation of source packages

As this will take some time, we need to ensure the current documents are clear on how to deploy source packages

[azlam-abdulsalam]

There have been significant changes for this issue. We are introducing an Install Source Package Task(only in azure pipelines to begin with), which will install the source package, Create Source Package is uplifted to bundle source along with the artifact and will support both checkout based model and install source package tasks