New command to add database source folder to workspace

[shati-patel]

Will fix #798.

As described in the linked issue, we don't have an easy way of re-adding a database's source folder to the workspace. This PR adds a new command (in the Databases View) that lets you re-add a source folder.

(We also considered re-adding source folders automatically, similar to how the codeQLDatabases.removeOrphanedDatabases command is run, but I'm now wondering if that'll be annoying to users. They may have deliberately removed a source folder from their workspace, and don't want it included automatically 🤔 I'm open to suggestions though!)

PS: In the process, I found a small bug in how we upgrade databases. (Opened an issue here #890, but haven't worked out how to fix that yet! 😅)

Checklist

• 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.
• @github/docs-content-codeql has been cc'd in all issues for UI or other user-facing changes made by this pull request.
  • I don't think a docs change is necessary, since the docs don't describe database commands in detail anyway. We just say the following, which is still valid 🙂

    To see the menu options for interacting with a database, right-click an entry in the list. You can select multiple databases using Ctrl/Cmd+click.

[aeisenberg]

Good point about users explicitly removing the source folder.

[aeisenberg]

Nicely done. This should have a changelog entry and then we can merge it.

[shati-patel]

Nicely done. This should have a changelog entry and then we can merge it.

Thanks for the review! I've checked the docs for changes (none needed) and updated the changelog 📝

[aeisenberg]

👍🏼