tests(helpers): separate db functions

[chronolaw]

Summary

KAG-5322

• The original dcdp and PLUGINS_LIST now turn to functions, since they are initialized in get_db_utils().
• Add a param extra_fields for the function validate_plugin_config_schema() to be compatible with EE
• move conf out of shell module

Checklist

• The Pull Request has tests
• A changelog file has been created under changelog/unreleased/kong or skip-changelog label added on PR if changelog is unnecessary. README.md
• There is a user-facing docs PR against https://github.com/Kong/docs.konghq.com - PUT DOCS PR HERE

Issue reference

Fix #[issue number]

[team-gateway-bot]

Cherry-pick failed for master, because it was unable to cherry-pick the commit(s).

Please cherry-pick the changes locally.

git remote add upstream https://github.com/kong/kong-ee
git fetch upstream master
git worktree add -d .worktree/cherry-pick-13618-to-master-to-upstream upstream/master
cd .worktree/cherry-pick-13618-to-master-to-upstream
git checkout -b cherry-pick-13618-to-master-to-upstream
ancref=$(git merge-base 1989ea7091b3cb191a6eeea6928f2493d798cefb d7834912bd7b1fee007163663da66b298019fcdb)
git cherry-pick -x $ancref..d7834912bd7b1fee007163663da66b298019fcdb