Rename dbconfig file to workspace-databases.json

[shati-patel]

Gives this config file to a more helpful name (similar to workspace-query-history.json).

Checklist

N/A - internal only 🤫

• CHANGELOG.md has been updated to incorporate all user visible changes made by this pull request.
• Issues have been created for any UI or other user-facing changes made by this pull request.
• [Maintainers only] If this pull request makes user-facing changes that require documentation changes, open a corresponding docs pull request in the github/codeql repo and add the ready-for-doc-review label there.