Leverage nvim-dap-go for test debugging

[fredrikaverpil]

Blocked by https://github.com/leoluz/nvim-dap-go/pull/81

• Auto-setup nvim-dap-go and provide it with a cwd for successful dlv debugging of test in Go sub-project.
• Add configuration options for nvim-dap-go.
• Resets nvim-dap-go inbetween test debug sessions, so to avoid a "sticky" cwd.

Needs overall cleanup and refactoring to make the whole project more readable and testable... but that will come later.