Add operation to create a pull request from local config changes

[netomi]

It would be handy to have an operation that can automatically create a PR in the respective organization for local changes. @fredg02

[netomi]

Here is an example of such a PR: eclipse-csi/.eclipsefdn#16

It has been created like that:

tn@proteus:~/workspace/eclipse/EclipseFdn/otterdog-configs$ otterdog open-pr eclipse-csi -b test -t "Test PR" -a netomi

Open PR for local configuration changes:

Organization technology.csi[id=eclipse-csi]
  created pull request #16 at https://github.com/eclipse-csi/.eclipsefdn/pull/16

[netomi]

I dont use the git config to determine the author for which the PR was created as this looks weird in the ticket. Its better to specify your github handle when running the operation.