Pyomo.DoE: Handle edge case where the nominal value for a parameter is zero

[adowling2]

Fixes # .

Summary/Motivation:

• If a parameter has a nominal value of zero, we will get a divide by zero error when calling compute_FIM

Changes proposed in this PR:

• Added a minimum step size for perturbation.

TODO Before converting from draft

• [ ] Finish edits and debug
• [ ] Decide where to add check to throw error if we try to use parameter scaling and a parameter is zero
• [ ] Add tests to check this edge case include any new error message
• [ ] Update documenation (minor)

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[adowling2]

@djlaky @smondal13 @sscini FYI