Support & Aligment of 504 Exception in CAMARA APIs

[PedroDiez]

Problem description

Currently in CAMARA APIs the indication of Exception 504 (TIMEOUT) in APIs YAMLs is not aligned.

There are some APIs that document it whilst in others are not documented.

The exception is already documented in CAMARA_common.yaml

And it is a scenario that may happen in any API.

Possible evolution

Aligned in every CAMARA WG to document this excepction in every APIs endpoints

Alternative solution
N/A

Additional context
Background discussion in: #189 (comment)

A child issue of this generic one is #291

[PedroDiez]

cc @rartych, @bigludo7

[bigludo7]

Hello @PedroDiez
Works for Orange team.