Allow ignoring of missing documents (404) for get and delete

[joosterman]

Change

This PR adds functionality to the get and delete method adhere to the ignore parameter in case the document is not found. Previously a NotFoundError was raised. Now we check if we need to ignore 404 errors and if so, simply return an object where the found flag is False.

Documentation: https://elasticsearch-py.readthedocs.io/en/latest/api.html#ignore

[joosterman]

I now implemented ignoring for the obvious two candidates. However ignoring in ES works for more than these. Basically in all cases we throw a NotFoundError the ignore=404 should result in a valid JSON response with the error field set.

@vrcmarcos What are your thoughts on making ignoring complete for the currently mocked functions?

[vrcmarcos]

Awesome addition, @joosterman ! The last time I used elasticsearch was 3 yeras ago, I was not aware of that feature. Don't even known if it is an old feature or not.

If ES supports on more methods, it make sense to add it to the other mocked functions too! Your PR looks great! Will merge it