Edited "admin manual"
Edited "admin manual"

Added a warning section on importance of identical configs for HA
configuration

- Closes #1135

gravitational/teleport,gravitational/teleport,yacloud-io/teleport,sokoow/teleport,yacloud-io/teleport,yacloud-io/teleport,sokoow/teleport,yacloud-io/teleport,gravitational/teleport,yacloud-io/teleport,sokoow/teleport,yacloud-io/teleport,sokoow/teleport,yacloud-io/teleport,gravitational/teleport,sokoow/teleport,sokoow/teleport,gravitational/teleport,gravitational/teleport