Add content providers to the portal

[ninanorgren]

In TeSS, you can add content providers at https://tess.elixir-europe.org/content_providers, which you can later choose when creating a new course. This will then be shown in the left side of the course information page. This should be possible to add directly in our portal.

• Test adding a provider
• Test adding a provider to a course

[harshita3199]

PR is merged to develop for this issue