Deprecate API fields using confidential notes

As part of Internal Notes: Technical debt cleanup (#363801 - closed) we need to complete the following tasks

• We do expose and accept confidential parameter to create notes on REST API https://gitlab.com/gitlab-org/gitlab/-/blob/a0e7625d059da069f47af514b41fd66c50dca260/lib/api/notes.rb#L76
• GraphQL also exposes confidential attribute and accepts it as an argument to create confidential notes: https://gitlab.com/gitlab-org/gitlab/-/blob/a0e7625d059da069f47af514b41fd66c50dca260/app/graphql/mutations/notes/create/base.rb#L21
• NotesController accepts this parameter to create internal notes on internal API.

We have to deprecate old fields and add the new fields as aliases for these endpoints in the same release, then on the next release frontend can start using the new fields to avoid breaking changes because of backwards compatibility.