feat(checkout,order): add placed order selector and facade in checkout

[griest024]

PR Checklist

Please check if your PR fulfills the following requirements:

• [x] The commit message follows our guidelines: https://github.com/graycoreio/daffodil/blob/master/CONTRIBUTING.md#commit
• [x] Tests for the changes have been added (for bug fixes / features)
• [x] Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[ ] Bugfix
[x] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Other... Please describe:

What is the current behavior?

The order package contains placed order behavior.

What is the new behavior?

The checkout package contains placed order behavior.

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[lderrickable]

I thought the plan was to delete the checkout package. Not true?

[griest024]

I thought the plan was to delete the checkout package. Not true?

Originally we had no use for it but @damienwebdev pointed out that "placed order" stuff that introduces a dep on cart makes more sense in checkout than order. Order is strictly for order entities and has no relation to cart.