graphql pagination: add PostProcessOptions
graphql pagination: add PostProcessOptions

This commit adds a PostProcessOptions options struct to be used by
manually paginated resolvers to instruct thunder to perform additional
postprocessing on the output based on input arguments.

As first options, this commit adds ApplyTextFilter and
SetPaginationInfo.

samsarahq/thunder,samsarahq/thunder,samsarahq/thunder,samsarahq/thunder,samsarahq/thunder