add additional header title validation

[peetucket]

Why was this change made?

Fixes #4492 - prevent malformed title header columns from being considered valid

WIP, as the validation may change

HOLD for testing on QA

How was this change tested?

• New specs
• Example bad spreadsheet runs ok on stage, but shows this on QA with this PR deployed:

[peetucket]

Not sure what the deal is with the test drop coverage. Every new line of code is covered.