Remove pkg directory

[imjasonh]

WDYT about moving everything under pkg up a level, so it's chainguard.dev/sdk/auth/aws, chainguard.dev/sdk/events/admission, chainguard.dev/sdk/uidp, etc.?

There's no conflict with proto, and it makes importpaths a little smaller and tidier. I'm not sure what kind of downstream breakages/refactors this would entail, but it's probably easier to do it now than later, if we ever want to do it.

[cmdpdx]

Good call out, I didn't consider this when moving out of mono. I have a PR I'm working on that switches refs in mono to use the public sdk. I've held off since @hectorj2f mentioned he had a proto change he wanted to get in before a new release of sdk. I can make this directory change and roll the path changes into my mono PR.

[hectorj2f]

My PRs got merged. So I am good, as long as we use the sdk latest version of main.