Backend: Add an optional description field under input
### Problem 1. Users don't know what the purpose of each input is 2. We want to display input information in the catalog by default ### Solution Add a description field underneath inputs. Suggested syntax: ```yaml spec: inputs: environment: default: production description: Deployment environment to use ``` [MR](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/132040) addressing this issue. Follow up issue - extract the description and present it in the CI/CD components catalog
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