Establish /library and /src directory structure

[ctab]

Implementing the directory structure for the tooling proposal:

1. Moved src.rego and src_test.rego files to /src (with same directory structure as library/)

2. Moving the sample constraints and any examples to library/<group>/<policy>/samples/<constraint name> directory.

3. Renamed and slight edits to example files:

• Renamed examples to example_disallowed.yaml¹ and made an example_allowed.yaml for some cases where the example had a comment showing what to switch to make it pass.
• Example resources all now have "disallowed" or "allowed" in the name.
• Some of the examples depended on a pre-existing namespace "production"; I switched these to use "default" so they could be applied as is.

¹ These were originally disallowed_example.yaml and allowed_example.yaml in the proposal doc; I switched it around when I started making them and realized that example_disallowed.yaml and example_allowed.yaml would be next to each other when listing the directory contents, whereas the other format would split them around constraint.yaml.

[maxsmythe]

LGTM, @ritazh @sozercan thoughts?

[sozercan]

we are missing some allowed examples for PSPs (like users, volumes, selinux, proc-mount etc) do we want to get to this in this PR or in a follow up?

[ctab]

@sozercan that's true. I was hoping to handle that in a separate PR so it would be easier to see new code vs. existing code.

[maxsmythe]

+1 to minimizing deltas in a PR of this scale.