Add TSIGKeys API

[Avarei]

implements #69.

First time writing unit/integration tests. I hope they are alright.

I'm also not sure if my implementation of

tsigkey, err := pdns.TSIGKey.Change(ctx, "examplekey.", powerdns.TSIGKey{
	Key: powerdns.String("newkey"),
})

fits the general style.
Looking forward to your feedback. Any feedback is appreciated :)

[joeig]

Hi @Avarei, thanks for your contribution.

Looks good to me, just some minor typos or naming suggestions. Please rebase against main to fix an issue with two pipeline actions.

[Avarei]

thank you for your feedback. I implemented it.

but appearantly I have a misunderstanding on how testing works.
I have to take a closer look on how to write the tests so they work with a mock server, as well as a real one reliably.

[Avarei]

I made some adjustments to the tests and make test and make test-without-mocks are successful now.

[joeig]

Thanks!