Added a workflow to update a POEM's status to 'Integrated'

[swryan]

• A new workflow, update_integrated, has been added

  • this is triggered via workflow_dispatch and takes the POEM number as an input
  • the workflow can be run manually to transition a POEM status to Integrated
  • the openmdao_update_poem workflow on the OpenMDAO repository may also trigger this workflow

• the versions of the checkout and setup-python helpers have been changed to more current versions

• a .gitignore file has been added to prevent temporary files being commited to the repository