[web] Rename InitialKeyserverInfo -> WebInitialKeyserverInfo

Summary:
Similar to previous diffs, but for InitialKeyserverInfo.

We're giving the type Web* prefix to prepare for being moved to lib along with WebInitialReduxStateResponse.

Depends on D10893

Test Plan: flow + CI + read through changes. Made changes with IDE Refactor -> Rename tool.

Reviewers: ashoat, ginsu, tomek

Reviewed By: ginsu

Differential Revision: https://phab.comm.dev/D10894