[BE] GraphQL: Update PipelineType in order to provide immediate feedback to editor

This is the backend issue for #280829 (closed)

• Update PipelineType to have either the iid or the sha as required. This needs to be done in order to make the pipeline searchable by sha.
• Add shortSha and the path (TBD) fields to PipelineType

This is what we want to accomplish:

project(fullPath: $fullPath) {
  pipeline(sha: $sha) {
     shortSha
     path (name TBD)
  }
}

This page may contain information related to upcoming products, features and functionality. It is important to note that the information presented is for informational purposes only, so please do not rely on the information for purchasing or planning purposes. Just like with all projects, the items mentioned on the page are subject to change or delay, and the development, release, and timing of any products, features, or functionality remain at the sole discretion of GitLab Inc.