setup/setup: fix `#:make-doc-index?` default

Making the default match the docs fixes Planet package installation,
which otherwise tries to rebuild the index too frequently.

Merge bug fix to v6.0 (pending review)
setup/doc-db: propagate read-only flag for database connection

Fixes a problem installation Planet packages under Windows,
for example, where attempting to open a read-only file in
write mode triggers an extremely slow result.

Merge bug fix to v6.0 (pending review)