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:

spec:
  inputs:
    environment:
      default: production
      description: Deployment environment to use

MR addressing this issue.

Follow up issue - extract the description and present it in the CI/CD components catalog