Workflow for upstream prebid sync

[khang-vu-ttd]

Create a workflow that

• gets the next highest tag as the current in package.json version
• gets all the commits between master and the prebid tag
• skips over commits that touch BidAdapter files
• also skips over commits that change version in package.json as they will have merge conflict since we added oaVersion to it
• create a branch called prebid-sync-[TAG VERSION]
• tries to apply remaining while keeping track which commits failed the merge
• if there is a merge conflict and its a test file or a bidAdapter file that was deleted in our repo, auto resolve conflict
• set version in package.json to updated tag and runs npm install to update package-lock.json
• creates a pull request with details about changes, example
• does a check that pull request hasn't already been created by previous run