Function isDidService

isDidService(obj): obj is DidService
Checks if a given object is a DidService.

A DidService in the context of DID resources must include the properties id, type, and serviceEndpoint. The serviceEndpoint can be a DidServiceEndpoint or an array of DidServiceEndpoint objects.
Parameters
- obj: unknown
  The object to be checked.
Returns obj is DidService
true if obj is a DidService; otherwise, false.
Example
```
const service = {
  id: "did:example:123#service-1",
  type: "OidcService",
  serviceEndpoint: "https://example.com/oidc"
};

if (isDidService(service)) {
  console.log('The object is a DidService');
} else {
  console.log('The object is not a DidService');
}
```