Support for multiple API clients

[bjornet]

As a developer, I want TTB to be able to scale to consume different API:s so that I can use it for different ticketing systems.

Acceptance Criteria

• it should add support for multiple API clients
• it should support Github API over Graphql
• it should support JIRA API over REST

Notes

• FYI: maybe JIRA uses the same interface (using Graphql) meaning that we might not need to abstract the client now. Or maybe it still has some differences, and thereby is best to do just that... That will become evident in this ticket. That is part of why this ticket exists.
• JIRA graphql: https://developer.atlassian.com/platform/atlassian-graphql-api/graphql/#examples

Epics

• Jira support #26