Add the option to configure the user who owns the pullrequest

[SierraNL]

By using this task we noticed there is a way around branch policies.
We use the task to connect two builds/branches together.
A user who made changes on branch1 and triggering the creation of this pullrequest is able to accept the pullrequest on branch2. This is possible because the pullrequest created by this task is owned by the Azure Devops Account who runs the actual build on the agent.

We would like to be able to set the owner of the pullrequest (with the user triggering the build), so we can close this loophole.