[ML] DF Analytics creation: ensure advanced editor validates model memory unit correctly

[alvarezmelissa87]

Summary

Ensures advanced editor validation correctly handles model_memory_limit values that are of type number as well as string.

Fixes issue where mml number type values were not converted to strings before attempting to validate the unit types - this caused a blank page due to an error in trying to uppercase a value of type number. We now convert to string prior to making the check.

Checklist

Use strikethroughs to remove checklist items you don't feel are applicable to this PR.

• This was checked for cross-browser compatibility, including a check against IE11
  - [ ] Any text added follows EUI's writing guidelines, uses sentence case text and includes i18n support
  - [ ] Documentation was added for features that require explanation or tutorials
• Unit or functional tests were updated or added to match the most common scenarios
• This was checked for keyboard-only and screenreader accessibility

For maintainers

- [ ] This was checked for breaking API changes and was labeled appropriately
- [ ] This includes a feature addition or change that requires a release note and was labeled appropriately

[elasticmachine]

Pinging @elastic/ml-ui (:ml)

[jgowdyelastic]

LGTM

[kibanamachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request
• Commit: 63f82b3

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream

[peteharverson]

LGTM