Add /notes endpoint to personal /snippets

Release notes

Problem to solve

The /snippets API endpoint for personal, no-project snippets does not include comments/notes, and has no /notes endpoint. Thus, it's not possible to retrieve note/comment content via the API.

Proposal

Similarly to project-level snippets, personal snippets should receive a /notes endpoint

• Update https://docs.gitlab.com/ee/api/snippets.html accordingly
• Review https://docs.gitlab.com/ee/user/snippets.html for a relevant update

Intended users

Everyone who uses personal snippets. See support/toolbox/dotfiles#30 for example.

Feature Usage Metrics

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