Return array of devfile errors rather than concatenated string
<!--IssueSummary start-->
<details>
<summary>
Everyone can contribute. [Help move this issue forward](https://handbook.gitlab.com/handbook/marketing/developer-relations/contributor-success/community-contributors-workflows/#contributor-links) while earning points, leveling up and collecting rewards.
</summary>
- [Close this issue](https://contributors.gitlab.com/manage-issue?action=close&projectId=278964&issueIid=564551)
</details>
<!--IssueSummary end-->
MR: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/202523+
NOTE: For context on MR heading, see: https://handbook.gitlab.com/handbook/engineering/devops/dev/create/remote-development/index.html#relationship-of-issues-to-mrs
## Description
TODO: Modify message support to return array of errors instead of joining the list into a single string.
Original thread: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/201038#note_2696531195
## Acceptance criteria
TODO:
* [x] \[Value being sent to GraphQL should be an array of errors.\]
## Implementation plan
TODO:
1. Change `message_support.rb` to return array of errors and `main.rb` to accept this array (Fix integration spec file)
2. Assert in GraphQL explorer that the endpoint returns an array of errors not an array containing one string element including all errors
issue