Add basic authentication

[olliesilvester]

The config server is running with the same permissions as dls-dasc, so we shouldn't allow it to be used by anyone in DLS.

For now, the easiest solution is to add an ingress rule, using something like https://kubernetes.github.io/ingress-nginx/examples/auth/basic/. Each beamline cluster will need need valid credentials, using secrets.

Acceptance Criteria

• Ingress rule added to helm chart
• Document how to give a new beamline cluster valid credentials

[olliesilvester]

Discussed with @DominicOram . Since we are using a whitelist, we can probably get away with not doing this urgently - as long as we are careful with what goes in the whitelist (for mx that's easy, it's just /dls_sw/ixx/software/daq_configuration)

[DominicOram]

To be more explicit I would say:

• Never put anything confidential in the config server (we should plaster that all over the docs)
• Everyone is able to read anything from here, writing is a different matter