feat(core): add error to DaffState

[griest024]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/graycoreio/daffodil/blob/develop/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• 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 new behavior?

Adds an error state to DaffState. While we initially decided that this was redundant beacuse an app dev can check the daffErrors property to determine if the state is an error, the DX of this actually sucks. For example, consider binding the status of a toast to the state of an entity. Without this, it requires all sorts of unnecessary code and logic.

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information