fix: not schema error message

[p-spacek]

What does this PR do?

adds the possibility to customize errorMessage for not schema
using the same approach schema.errorMessage || localize(... as elsewhere

so it's possible to write:

   {
      not: {
        properties: {
          prop1: {
            type: 'number',
          },
        },
        errorMessage: 'prop1 must not be a number',
      }
    }

Is it tested? How?

manually, the same approach is already used elsewhere

[coveralls]

coverage: 84.148% (-0.03%) from 84.174%
when pulling 776da85 on jigx-com:fix/not-schema-error-message
into 7203630 on redhat-developer:main.

[msivasubramaniaan]

@p-spacek please rebase the repo