Add SprintIssues Stream

[akoebbe-uu]

Currently, this tap has a SprintStream and an IssueStream, but no SprintIssueStream to show the issues that are in each sprint. This is done in the Airbyte variant here by using the sprint/{sprint_id}/issue api endpoint. This would be similar to how the SprintStream is fetched by board_id.

It is certainly possible to add the sprint and closedSprint fields on to the IssueStream and derive the table from those values, but it would be inefficient from a storage standpoint.