Tester needs to accept a page size argument

[jeffhandley]

Related to #97, the dotnet/dotnet-api-docs training resulted in timeouts trying to download pull requests through Tester. Tester does not accept an argument for page size though, so this could not be worked around.

This would need:

1. Tester to accept --pull-page-size and --issue-page-size arguments
2. The test-pulls.yml and test-issues.yml workflows to accept page_size inputs and pass them through
3. The train.yml workflow to accept these inputs and pass them through (unless we hit the max inputs limit)