Script server: Allow read-only access

Currently NICOS can be accessed through a password protected ActiveMQ queue, the password for which could be served up as described in https://github.com/ISISComputingGroup/IBEX/issues/1995. This will be the method for read/write access.

A separate access method should be created that allows read only access to NICOS. To do this we need to:
- [ ] Add a read-only script server queue to our activeMQ config
- [ ] Create a read-only account in the NICOS config
- [ ] Modify the script server proxy to accept commands from the new queue and log in to NICOS under the read-only account

A follow up ticket will configure the GUI to use this.