Document label scopes required for scoped tokens

[oiahoon]

Summary

• add the granular read and write label scopes to the publishing permissions reference
• keep the scoped-token setup guide synchronized with the same requirements

The Confluence content-label endpoint requires both read:label:confluence and write:label:confluence when adding labels with granular scopes.

Fixes #1187

Verification

• python -m sphinx -M html doc /tmp/confluencebuilder-html -E -a -W --keep-going
• verified both generated HTML pages contain both scope identifiers
• git diff --check

[jdknight]

Thanks for closing this one up for everyone. 🙇