Add create mutations from artist

[aonomike]

What does this PR do?

Add create artist mutation so that artists can be created by sending a mutation query and variables to the api endpoint

What are the relevant Github Issues ?

Fixes #89

[sourcelevel-bot[bot]]

SourceLevel has finished reviewing this Pull Request and has found:

• 1 possible new issue (including those that may have been commented here).

You can see more details about this review at https://app.sourcelevel.io/github/AgileVentures/sing_for_needs/pulls/108.