`You are not authorized to use this endpoint` is returned instead `Domain does not exist` is never returned` when domain is not in DB

[mendeleden]

When calling set-domain we first check if the API key is valid for the the domain thus inherently check if the domain is in the DB.

When a new use attempt to call set-domain he should be informed via error message to use to enable-domain endpoint, i.e.

 "Domain does not exist. Please use /enable-domain." 

since we first check the api key and not whether the domain is in the DB we don't return the correct error to the caller.

Acceptance Criteria:

1. rewrite the logic for set-domain (and other endpoints) which should first check if the domain is not registered with namestone and display the correct error message to the user.
2. add tests in set-domain.tests.js to cover this testcase

[mendeleden]

the same issue occurs for get-names , response code is 400 instead of 401 when using incorrect api key for a fetching a specific domain`,

[mendeleden]

the same issue occurs for search-names if the domain does not exists, we return error code 401 saying You are not authorized to use this endpoint because the api checks run first before we verify the domain exists