OwlLoadTask: Provide support for optional user/password authentication credentials.

[NicolasRouquette]

User Story

As a user, I would like support for SPARQL endpoint authentication credentials so that I can use a SPARQL endpoint that requires authentication..

Detailed Description

Description providing additional details and context.

Add optional username and password to OwlLoadTask.

Acceptance Criteria

• [ ] Given OwlLoadTask with username and password and an authentication-based SPARQL endpoint, then OwlLoadTask successfully uploads data

[NicolasRouquette]

Fixed in PR #49