Add 403 example for Invalid Token Context

[bigludo7]

Problem description
Have a specific 403 example to tacke the case when the msisdn obtained from the network in the authorization first step (and passed in the token) is distinct from the one we get in the POST payload. discussed here: #70

Possible evolution
Add in 403 examples part

              value:
                status: 403
                code: INVALID_TOKEN_CONTEXT
                message: Phone number cannot be deducted from access token context

Alternative solution

Additional context