Add ability to search Releases in the GraphQL API

Summary

It's currently possible to list all releases using this query:

query{
  project(fullPath:"gitlab-org/gitlab"){
    releases {
      nodes {
        name
        description
      }
    }
  }
}

However, it's not possible to search the list of releases. In order to support issue lists in Vue we need to add this behavior to the GraphQL API.

See #326474 (comment 541910820)