nanobsd: Clean up target pkg database and metalog after install

[senguptaangshuman17_gmail.com]

Summary

Add _xxx_fix_pkg_permissions to fix the libsa.3.gz and /root permissions in the target pkg database until pkg metalog generation is fixed upstream, pkg_db_vacuum to verify and compact the target pkg database after the manual SQL edits, and _xxx_pkg_add_var_db_files_to_metalog to add the generated /var/db/pkg files to the metalog.

Also document _xxx_pkg_metalog's existing permission fixups by referencing the same upstream pkg issue.

[senguptaangshuman17_gmail.com]

Clean up merge conflict markers in defaults.sh

[senguptaangshuman17_gmail.com]

Rebase stack on top of D59043 update

[jlduran]

I think _xxx_pkg_db_dump_or_vacuum should be added sooner. In fact, I think this function should not be a _xxx_ function, as we will always want to verify the integrity of the pkg database before shipping our NanoBSD image, so I suggest "promoting" it to a regular pkg function (pkg_db_vacuum since it no longer dumps.) and including it in D58951.
I think the commit message in this revision also needs updating.

[senguptaangshuman17_gmail.com]

Update cleanup helper to call pkg_db_vacuum