Split shovel into muliple files

[snichme]

WHAT is this pull request doing?

Separate each component of the shovel feature into separate files. No functionality changes just moved the code into files to make it easier to browse it.

[viktorerlingsson]

should this just be an empty abstract class?

[snichme]

Yes, the idea is that the Shovel::Runner takes a Source and a Destination the destination has abstract methods and it works since we already have three destinations implemented.

For Source we only have one implementation so we dont know what might be a good interface, but we can still use the abstract class in the runner and rely on duck typing.

[viktorerlingsson]

There's some lint errors (not_nil! usage) that already existed prior to this refactor, but maybe they should be addressed?

[snichme]

There's some lint errors (not_nil! usage) that already existed prior to this refactor, but maybe they should be addressed?

I want this PR to just be a split of files. Addressing the not_nil! should be done but at some other change