Set db tree item context value to drive actions

[charisk]

The various context menu actions that we want to add for the new db panel should only be visible under certain conditions (mostly based on the db item kind). This change updates the contextValue of db tree view items to include strings like canBeSelected, canBeRemoved etc. so that the command can easily check if the action should be allowed for a specific tree view node or not using a regex match.

Checklist

N/A:

• 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.

[norascheuch]

🚀