Add confidential attr to graphQL for notes update

What does this MR do?

It adds confidential attribute to the graohQL for notes update.

Note creation and public API changes have been/will be submitted as separate MRs.

Related MRs

• Update Service preparation
• Set notes confidentiality during creation graphQL
• Set notes confidentiality during creation API

Screenshots

Request example

mutation {
  updateNote(input: {id: "gid://gitlab/Note/1744", confidential: true}) {
    note {
      confidential
      body
    }
  }
}

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• [-] Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.

Issue: #207473 (closed)