Add ability to set api url dynamically

[RChandler234]

Description

Jack wants to be able to point the client at different backend URLs without having to rebuild Argos. Ideas for this are passing the argument in through nginx arguments or passing it in through the UI and using some sort of global state (probably this: https://ngrx.io/guide/signals/signal-store)

Acceptance Criteria

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Proposed Solution

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Mocks

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