Introduce WikiListPages RPC function
Related issue: https://gitlab.com/gitlab-org/gitlab-ce/issues/53523
This MR is to solve the problem, which !238 (closed) started to solve, but it's just more convenient to create a new MR than rebase that one
This MR introduces WikiListPages
function which uses WikiGetAllPagesRequest
and returns WikiListPagesResponse
Edited by Igor Drozdov