add clarifications in permissions docs (discord#7332)

* add descriptions for channel types

* update ADD_REACTIONS and USE_EMBEDDED_ACTIVITIES table entries

* npm run fix:tables

* fix table

* add channel type mapping

* Update docs/topics/Permissions.md

Co-authored-by: advaith <[email protected]>

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Co-authored-by: advaith <[email protected]>

Author: 2 people