Disable some functionality when the backend is down

[gsproston-scottlogic]

Bug report

Description

When the backend is down, the user can still use some of the features on the frontend which simply won't work without the backend.
We want to instead disable some features or show error messages.

Reproduction steps

Steps to reproduce the behavior:

1. Don't run the backend.
2. Start the frontend.
3. The user can still attempt to do things like send messages and view documents.

Expected behavior

The expected behaviour depends on the feature...

• Sending chat messages - User should not be able to send messages, disable the send button. - don't do this as we need to know when the backend is running again.
• Show error when unable to get documents to view #712
• Show error in the handbook if we fail to get system roles #713
• Show error if we fail to reset defences #714

Screenshots

This is what the document viewer looks like when the backend isn't running:

System roles in the handbook:

Resetting defence configurations:

Software (please complete the following information):

• Browser: Edge

Additional context

Questions:

• Are there other features that need looking at?
• Are we happy with the suggested expected behaviours? - yes, refined

Acceptance criteria

TBD once questions are answered.

[gsproston-scottlogic]

Split into smaller tickets