[Cases] Inconsistency in the Cases form regarding the "Save" button and validation

[cnasikas]

In Cases, we use forms a lot to create and update cases. There are Inconsistencies between different forms in Cases regarding control buttons (Save/Cancel) and validation. We should audit all cases forms and apply @mdefazio guidance:

• Do not prematurely display errors: Keep submit button active initially, even if a required field is empty
• Disable submit if the form has errors: Disable the submit button if a field is filled and has an error (or was clicked and fields were left empty)
• Validation: Do validation on blur if a field has incorrect input (such as using characters that aren’t allowed).
• Loading state: Disable save button during loading state

Most of the guidance is already applied by the EUI form lib. In some instances, we disable the submit button when we should not.

[elasticmachine]

Pinging @elastic/response-ops (Team:ResponseOps)

[elasticmachine]

Pinging @elastic/response-ops-cases (Feature:Cases)

[mdefazio]

Do not prematurely display errors: Keep submit button active initially, even if a required field is empty

As much as I like this one, and has sound reasoning, I believe this goes against the html5 default behavior for required fields. I'm open to discussing some options, but I imagine this one is more complicated.