fix: Add ValidationMetadata.name to IsOptional

[Clashsoft]

Description

This makes it easier to detect the presence of the IsOptional decorator.

Checklist

• the pull request title describes what this PR does (not a vague title like Update index.md)
• the pull request targets the default branch of the repository (develop)
• the code follows the established code style of the repository
  • npm run prettier:check passes
  • npm run lint:check passes
• tests are added for the changes I made (if any source code was modified)
• documentation added or updated
• I have run the project locally and verified that there are no errors

Workaround

The presence of the IsOptional decorator, given ValidationMetadata, can be checked with a blackbox test of the constraint.

  isIsOptional(m: ValidationMetadata) {
    if (m.type !== ValidationTypes.CONDITIONAL_VALIDATION) {
      return false;
    }
    const constraint = m.constraints?.[0];
    // black box testing
    return constraint
      && constraint({[m.propertyName]: null}, null) === false
      && constraint({[m.propertyName]: undefined}, undefined) === false
      && constraint({[m.propertyName]: ''}, '') === true
      && constraint({[m.propertyName]: ' '}, ' ') === true
      && constraint({[m.propertyName]: 0}, 0) === true
      && constraint({[m.propertyName]: false}, false) === true
      && constraint({[m.propertyName]: true}, true) === true
      ;
  }

[Pigrabbit]

I'm looking forward to getting this PR to be merged 👀

[Clashsoft]

I'd like to bump this. It is a simple change without any potential negative impact.

[braaar]

Thanks for the contribution!

[github-actions]

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