[lib] refactor connection-related actions in keyserver-reducer to ops

Summary:
Convert logic to ops approach.

Depends on D10770

Test Plan:
This is not that easy to test, and this sie basically copy-pasting approach from rest of the stack so this time just carefully reading the code.

EDIT: tested by dispatching following from redux dev-tools:

{
  type: 'SET_LATE_RESPONSE',
  payload: { messageID: '256|5', isLate: true, keyserverID: '256' }
}
{
  type: 'UPDATE_DISCONNECTED_BAR',
  payload: { visible: 'true', keyserverID: '256' }
}
{
  type: 'SET_CONNECTION_ISSUE',
  payload: { connectionIssue: null, keyserverID: '256' },
}

Reviewers: inka

Reviewed By: inka

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D10771