Improve UX for error messaging for dynamic inputs
The following discussion from !214046 should be addressed:
- [ ] @avielle started a [discussion](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/214046#note_2913046661): (+2 comments)
> In the example config from the MR description, this input:
>
> ```yaml
> # Level 3: Depends on environment + deployment_type
> canary_percentage:
> description: 'Canary rollout percentage'
> rules:
> - if: $[[ inputs.deployment_type ]] == 'canary' && $[[ inputs.environment ]] == 'production'
> options: ['10', '25', '50', '75']
> default: '25'
> - if: $[[ inputs.deployment_type ]] == 'canary' && $[[ inputs.environment ]] == 'staging'
> options: ['50', '100']
> default: '50'
> - if: $[[ inputs.deployment_type ]] == 'canary'
> options: ['100']
> default: '100'
> - options: []
> ```
>
> is giving me this error in the CI editor
>
> ```
> This GitLab CI configuration is invalid: `canary_percentage` input: `` cannot be used because it is not in the list of allowed options
> ```
>
> Is that what we expect?
issue