add portalconfig related api calls to tgsearch client
these are (https://textgridlab.org/1.0/tgsearch-public/portal/api-docs?url=/1.0/tgsearch-public/portal/openapi.json):
- /portal/projects
- /portal/project/{id}
- /portal/toplevel/{id}
whats to think about: how to deal with json vs xml databinding, as these APIs are able to provide both via content negotiation