Adds a per-organization setting to disable workspace sharing. When enabled,
all existing workspace ACLs in the organization are cleared and the workspace
ACL mutation API endpoints return `403 Forbidden`.
This complements the existing site-wide `--disable-workspace-sharing` flag by
providing more granular control at the organization level.
Closes https://github.com/coder/internal/issues/1073 (part 2)
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Co-authored-by: Steven Masley <Emyrk@users.noreply.github.com>