DEVEXP-1107: Export domain API classes

[asein-sinch]

No description provided.

[JPPortier]

Is this PR is an initial step regarding opening access to domain for MCP?
Current domains implementation/init are tied to ApiFecthClient (e.g.: https://github.com/sinch/sinch-sdk-node/blob/DEVEXP-1107_Export-domain-API-classes/packages/numbers/src/rest/v1/numbers-domain-api.ts#L63)
Ideally, and this is highlighted by having client field public (https://github.com/sinch/sinch-sdk-node/blob/DEVEXP-1107_Export-domain-API-classes/packages/numbers/src/rest/v1/numbers-domain-api.ts#L13), the classes should use dependencies injection and then client could private.
Then, no need more need for this https://github.com/sinch/sinch-mcp-server/blob/main/src/tools/verification/utils/verification-service-helper.ts#L36
Then, "just" initialize the ApiService with proper dedicated ApiFetchClient

[asein-sinch]

I planned to let it this way, but if we want to implement what you are proposing, it must be done in the same release, and so I'll group everything in the same PR.
To keep in mind regarding the current design: it has been done this way to support the lazy loading of the credentials. I can move the lazy loading up to the service class, but it would break the current implementation of the Domain API since the constructor would now expect a getClient() callback instead of the list of parameters