Add new field webUrl to Code Quality APIs

What does this MR do and why?

Adds a new field webUrl to the Code Quality's GraphQL and private API (codequality_reports.json) response. This will help move the logic of building the path from the frontend to the backend.

Relevant issue: #355426 (closed)

Screenshots or screen recordings

REST API

GraphQL

How to set up and validate locally

1. Start Gitlab (gdk start)
2. Create a repository, add some code and enable Code Quality
3. Create an MR and check the response:
   1. <group>/<repository>/-/merge_requests/<mr_id>/codequality_reports.json. Alternatively, open the MR page and append /codequality_reports.json to the URL
   2. Use the below GraphQL query in the GraphQL Explorer (-/graphql-explorer)

GraphQL Query

query {
  project(fullPath: "<group>/<repository>") {
    pipeline(iid: <mr_iid>) {
      codeQualityReports(first: 2, after: "") {
        count
        edges {
          node {
            line
            description
            path
            fingerprint
            severity
            webUrl
          }
        }
        pageInfo {
          startCursor
          endCursor
          hasNextPage
        }
      }
    }
  }
}

MR acceptance checklist

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